General Science Practice Test

The interactive test above draws from this bank in random order. Every question also has its own page with the full explanation.

1. What is the basic unit of life?

   • Atom
   • Cell ✓
   • Organ
   • Tissue

   The cell is the basic structural and functional unit of all living organisms. Cell theory (one of biology's foundational principles): (1) All living things are composed of one or more cells; (2) The cell is the basic unit of life; (3) All cells come from pre-existing cells. Levels of biological orga… Full explanation →

2. What process converts sunlight, water, and carbon dioxide into glucose and oxygen?

   • Photosynthesis ✓
   • Respiration
   • Digestion
   • Transpiration

   Photosynthesis occurs in plants, algae, and some bacteria, converting light energy into chemical energy stored in glucose. Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Plants take in CO₂ through stomata in leaves; absorb water through roots; capture light using chlorophyll in chloroplasts (… Full explanation →

3. Which type of blood vessel carries blood AWAY from the heart?

   • Capillary
   • Venule
   • Vein
   • Artery ✓

   Arteries carry blood AWAY from the heart (think: A for Away, A for Artery). Veins carry blood TOWARD the heart. Capillaries are tiny vessels between arteries and veins where exchange of gases, nutrients, and waste occurs. Arterial vs venous characteristics: (1) Arteries — thick muscular walls (withs… Full explanation →

4. What is the atomic number of an element?

   • Number of electrons in valence shell
   • Number of neutrons
   • Total mass
   • Number of protons in the nucleus — identifies the element ✓

   Atomic number = number of protons in the nucleus; uniquely identifies the element. Carbon has 6 protons (atomic number 6); oxygen has 8; iron has 26. The periodic table is organized by atomic number, increasing left-to-right and top-to-bottom. Atoms also contain: (1) Neutrons — in the nucleus, no ch… Full explanation →

5. What is the chemical formula for water?

   • CO₂
   • O₂
   • H₂O ✓
   • H₂O₂

   Water = H₂O = 2 hydrogen atoms + 1 oxygen atom. Common chemical formulas to know: H₂O (water); CO₂ (carbon dioxide); O₂ (oxygen gas); N₂ (nitrogen gas); H₂ (hydrogen gas); NaCl (sodium chloride/salt); HCl (hydrochloric acid); NaOH (sodium hydroxide/lye); H₂SO₄ (sulfuric acid); NH₃ (ammonia); CH₄ (me… Full explanation →

6. What is the pH of a neutral solution like pure water?

   • 0
   • 14
   • 10
   • 7 ✓

   pH scale measures acidity/alkalinity from 0 to 14: pH < 7 = acidic; pH = 7 = neutral; pH > 7 = basic/alkaline. Pure water has pH 7. Logarithmic scale: each integer change is a 10-fold change in H+ concentration. So pH 4 is 10× more acidic than pH 5, 100× more than pH 6. Common substances and approxi… Full explanation →

7. What is Newton's First Law of Motion?

   • Force = mass × acceleration
   • Every action has equal and opposite reaction
   • Energy cannot be created or destroyed
   • An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted on by an external force (Law of Inertia) ✓

   Newton's three laws of motion: (1) FIRST LAW (Inertia): An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted on by a net external force. Objects 'want' to keep doing what they're doing; inertia is the resistance to change in motion. Mass measure… Full explanation →

8. What is the formula for force according to Newton's Second Law?

   • F = mv
   • F = ½mv²
   • F = ma ✓
   • F = mgh

   Newton's Second Law: F = ma. Force = mass × acceleration. Units: Force in Newtons (N); mass in kilograms (kg); acceleration in meters per second squared (m/s²). 1 Newton = 1 kg·m/s² (the force needed to accelerate 1 kg at 1 m/s²). Other common physics formulas: (1) Weight = mg (mass × gravitational … Full explanation →

9. Which of the following is a form of kinetic energy?

   • Energy stored in a battery
   • Chemical bonds
   • Energy of a moving object ✓
   • Gravitational potential energy

   Kinetic energy is the energy of motion. Any moving object has KE: KE = ½mv². Examples: a moving car, falling water, wind, a thrown ball, atoms vibrating (thermal energy), electrons flowing (electricity). Forms of energy: (1) Kinetic — motion energy (mechanical, thermal, sound, electrical); (2) Poten… Full explanation →

10. What is the order of planets from the Sun?

    • Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune ✓
    • Earth, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune
    • Mercury, Mars, Venus, Earth, Jupiter, Saturn, Uranus, Neptune
    • Venus, Mercury, Earth, Mars, Jupiter, Saturn, Neptune, Uranus

    Order from Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mnemonics: 'My Very Educated Mother Just Served Us Noodles' (replacing 'Nachos' since Pluto's reclassification). Pluto was reclassified as a dwarf planet in 2006. Planet categories: (1) Terrestrial (inner, rocky): Mercury… Full explanation →

11. What is the rock cycle?

    • Erosion only
    • Daily weather changes
    • Annual seasonal changes
    • The continuous process by which rocks transform between three types: igneous (from cooled magma/lava), sedimentary (from compressed sediments), and metamorphic (from heat/pressure transformation) ✓

    The rock cycle describes how Earth's rocks continually transform. Three rock types: (1) IGNEOUS — formed when molten rock (magma below ground, lava above) cools and solidifies. Intrusive igneous rocks cool slowly underground (granite, gabbro); extrusive cool quickly above (basalt, obsidian, pumice).… Full explanation →

12. What causes Earth's seasons?

    • The tilt of Earth's axis (23.5°) causes different parts of Earth to receive more or less direct sunlight throughout the year as Earth orbits the Sun ✓
    • The Sun moves north and south
    • Atmospheric changes
    • Earth's distance from the Sun varies

    Earth's seasons are caused by the 23.5° tilt of Earth's rotational axis relative to its orbital plane around the Sun. As Earth orbits, the tilt causes hemispheres to receive different amounts of direct sunlight at different times of year. Summer in a hemisphere: that hemisphere is tilted TOWARD the … Full explanation →

13. Which organ system is responsible for filtering blood and excreting waste through urine?

    • Urinary (renal) ✓
    • Digestive
    • Endocrine
    • Lymphatic

    Urinary/renal system: kidneys (2), ureters (2), bladder, urethra. Functions: (1) Filter blood to remove metabolic wastes (urea, creatinine, excess salts and water); (2) Regulate fluid and electrolyte balance; (3) Maintain blood pH; (4) Regulate blood pressure (renin); (5) Produce erythropoietin (sti… Full explanation →

14. What is the largest organ of the human body?

    • Lungs
    • Skin ✓
    • Liver
    • Brain

    Skin is the largest organ, with surface area ~1.5-2 square meters and accounting for ~15% of body weight. Skin (integumentary system) functions: (1) Barrier — protects against infection, dehydration, UV radiation, mechanical injury; (2) Thermoregulation — sweating cools body; vasodilation/constricti… Full explanation →

15. Where does most digestion and nutrient absorption take place?

    • Stomach
    • Mouth
    • Large intestine
    • Small intestine ✓

    The small intestine is where most chemical digestion and virtually all nutrient absorption occur. About 6-7 meters long in adults; three sections: duodenum (first 25 cm; receives bile from gallbladder and pancreatic enzymes), jejunum (next ~2.5 m; most absorption), ileum (final ~3.5 m; absorbs vitam… Full explanation →

16. What is the speed of light in a vacuum?

    • 3 × 10³ m/s
    • 3 × 10¹⁰ m/s
    • 3 × 10⁵ m/s
    • 3 × 10⁸ m/s (approximately 300,000 km/s or 186,000 miles/s) ✓

    Speed of light in vacuum (c) = 299,792,458 m/s ≈ 3 × 10⁸ m/s ≈ 300,000 km/s ≈ 186,000 mi/s. This is the universal speed limit per Einstein's special relativity — no information or matter can exceed it. Light slows in matter (water n=1.33, glass n=1.5, diamond n=2.4 — refractive index); the ratio c/v… Full explanation →

17. What is the difference between an element and a compound?

    • Elements are man-made; compounds are natural
    • There is no difference
    • Element: pure substance made of only one type of atom (e.g., oxygen, gold); Compound: pure substance made of two or more elements chemically bonded in fixed ratios (e.g., water = 2H + 1O) ✓
    • Elements are gases; compounds are solids

    Matter classification: (1) ELEMENT — pure substance of one type of atom, cannot be broken down by chemical means. ~118 known elements (~92 naturally occurring). Examples: gold (Au), oxygen (O₂), carbon (C), iron (Fe), helium (He). Listed on periodic table. (2) COMPOUND — pure substance of two or mor… Full explanation →

18. What molecule carries genetic information in cells?

    • DNA (deoxyribonucleic acid) — stores genetic instructions in sequences of four nucleotides (A, T, C, G) organized into genes on chromosomes ✓
    • Proteins
    • RNA only
    • ATP

    DNA (deoxyribonucleic acid) is the genetic material in all known living organisms. Structure: (1) Double helix — two strands wound around each other; (2) Nucleotides — building blocks; each contains a sugar (deoxyribose), phosphate group, and one of four nitrogenous bases: Adenine (A), Thymine (T), … Full explanation →

19. What is the unit of electric current?

    • Ampere ✓
    • Ohm
    • Volt
    • Watt

    Electric current is measured in Amperes (A or 'amps'). One ampere = one coulomb of charge per second. Key electrical quantities and units: (1) Current (I) — flow of charge — Amperes (A); (2) Voltage (V) — electrical potential difference — Volts (V); (3) Resistance (R) — opposition to current flow — … Full explanation →

20. What is the atmosphere primarily composed of?

    • About 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide, plus trace gases and variable water vapor ✓
    • Mostly hydrogen
    • Mostly oxygen
    • Mostly carbon dioxide

    Earth's atmosphere composition: nitrogen (N₂) ~78%; oxygen (O₂) ~21%; argon (Ar) ~0.9%; carbon dioxide (CO₂) ~0.04% (rising due to fossil fuels); water vapor variable (0-4%); trace gases (neon, helium, methane, krypton, hydrogen, ozone). Important: oxygen is only 21% — but it's enough to sustain lif… Full explanation →

21. What is mitosis?

    • Sexual reproduction process
    • Cell division producing two identical diploid daughter cells from one parent cell; used for growth, tissue repair, and asexual reproduction ✓
    • Production of gametes
    • Cell death

    Mitosis is cell division producing two genetically identical diploid daughter cells. Phases: (1) Prophase — chromosomes condense, nuclear envelope breaks down, spindle fibers form; (2) Metaphase — chromosomes line up at cell equator; (3) Anaphase — sister chromatids separate, pulled to opposite pole… Full explanation →

22. Which of the following is a chemical change?

    • Glass shattering
    • Ice melting to water
    • Wood burning to ash and smoke ✓
    • Sugar dissolving in water

    Chemical change: new substances are formed with different chemical properties; chemical bonds break and form. Wood burning: cellulose + oxygen → carbon dioxide + water vapor + ash; new substances produced; cannot easily reverse. Signs of chemical change: (1) Color change; (2) Temperature change (exo… Full explanation →

23. What is the difference between mass and weight?

    • Weight is more accurate
    • Mass: the amount of matter in an object (kg); constant regardless of location. Weight: gravitational force on an object (N); varies with gravity (you weigh less on the Moon, more on Jupiter) ✓
    • Mass is for solids, weight for liquids
    • They are identical

    Mass vs Weight — commonly confused: MASS: amount of matter in an object; measured in kilograms (kg) or grams (g); constant — same on Earth, Moon, or in space; measured using a balance (compares to known masses). WEIGHT: gravitational force on an object; measured in Newtons (N); varies with gravitati… Full explanation →

24. What is the function of red blood cells?

    • Carry oxygen from lungs to body tissues and carbon dioxide back to lungs; contain hemoglobin which binds oxygen ✓
    • Produce hormones
    • Fight infection
    • Form blood clots

    Red blood cells (RBCs/erythrocytes) — most abundant blood cells (~4-6 million per microliter). Primary function: gas transport. Hemoglobin: iron-containing protein; each hemoglobin molecule binds 4 oxygen molecules; gives RBCs and blood their red color. RBC characteristics: biconcave disc shape (inc… Full explanation →

25. What is plate tectonics?

    • The study of ocean currents
    • How rivers form
    • Climate patterns
    • The theory that Earth's lithosphere is divided into large plates that move slowly over the mantle, causing earthquakes, volcanoes, mountain building, and continent drift ✓

    Plate tectonics is the unifying theory of Earth's geological processes. Earth's lithosphere (crust + upper mantle) is broken into ~15 major plates (and many smaller ones) that move slowly (cm/year) over the asthenosphere (semi-fluid upper mantle). Plate boundary types: (1) DIVERGENT — plates move ap… Full explanation →

26. What is the unit of electrical resistance?

    • Volt
    • Watt
    • Ohm ✓
    • Ampere

    The Ohm (Ω) is the unit of electrical resistance. Ampere = current; Volt = voltage; Watt = power. A useful way to keep the four straight: the volt pushes, the ampere flows, the ohm resists, and the watt is the rate at which energy is used (volts × amperes). The symbol Ω (omega) is used for ohms on c… Full explanation →

27. What organelle is the 'powerhouse of the cell'?

    • Mitochondria ✓
    • Ribosome
    • Nucleus
    • Vacuole

    Mitochondria produce ATP (cellular energy) through aerobic respiration — the powerhouse of the cell. The mitochondrion breaks down glucose with oxygen to release energy stored as ATP, which powers almost everything the cell does. The distractors have other jobs: the nucleus stores DNA and controls t… Full explanation →

28. What is the approximate speed of sound in air at sea level?

    • 3,000 m/s
    • 1,126 m/s
    • 343 m/s ✓
    • 30 m/s

    Sound travels approximately 343 m/s (about 1,125 ft/s or 767 mph) in air at 20°C at sea level. Sound is a pressure wave that needs a medium, and its speed depends on that medium and the temperature — it travels faster in warmer air, faster still in water (about 1,480 m/s) and fastest in solids such … Full explanation →

29. Which blood type is the universal donor for red blood cells?

    • O negative ✓
    • B negative
    • AB positive
    • A positive

    O negative is the universal donor for red blood cells — it lacks A, B, and Rh antigens, making it compatible with all blood types. Full explanation →

30. What is the pH of a neutral substance?

    • 10
    • 0
    • 7 ✓
    • 14

    The pH SCALE: 0-14 scale measuring hydrogen ion concentration. pH 7 = NEUTRAL (pure water); pH below 7 = ACIDIC (more H+ ions); pH above 7 = BASIC/ALKALINE (more OH- ions). Each unit represents a 10x change: pH 6 is 10x more acidic than pH 7; pH 5 is 100x more acidic. COMMON pH VALUES: Battery acid … Full explanation →

31. What is Newton's Third Law of Motion?

    • The heavier the object, the less it accelerates
    • For every action, there is an equal and opposite reaction — if object A exerts a force on object B, object B exerts an equal force in the opposite direction on object A ✓
    • Force equals mass times acceleration
    • Objects in motion stay in motion

    NEWTON'S THREE LAWS: First Law (Inertia): Objects at rest stay at rest; objects in motion stay in motion, unless acted on by a net force. Second Law (F=ma): Force = Mass × Acceleration; more force = more acceleration; more mass = less acceleration for the same force. Third Law (Action-Reaction): For… Full explanation →

32. What is the function of DNA in a cell?

    • Contains the genetic instructions for building and operating the organism — DNA is the blueprint for protein synthesis and is passed from parent to offspring during reproduction ✓
    • Produces energy for the cell
    • Transports oxygen in the blood
    • Digests nutrients

    DNA (Deoxyribonucleic Acid) is the molecule that contains the GENETIC INSTRUCTIONS for every living organism. Located primarily in the NUCLEUS of cells. STRUCTURE: Double helix — two strands wound around each other; each strand made of nucleotides with four bases: Adenine (A), Thymine (T), Guanine (… Full explanation →

33. What causes the seasons on Earth?

    • Sunspot activity
    • The tilt of Earth's axis (approximately 23.5°) relative to its orbital plane — when the Northern Hemisphere is tilted toward the Sun, it receives more direct sunlight and has summer; when tilted away, it has winter ✓
    • Earth's varying distance from the Sun
    • The rotation speed of Earth

    SEASONS are caused by AXIAL TILT — NOT distance from the Sun. Common misconception: Earth is actually slightly CLOSER to the Sun during Northern Hemisphere winter. AXIAL TILT EFFECT: When the Northern Hemisphere tilts toward the Sun: sunlight strikes at a more direct angle (less spreading over area)… Full explanation →

34. Which part of the cell is known as the 'powerhouse' because it produces energy (ATP)?

    • Nucleus
    • Cell membrane
    • Mitochondria ✓
    • Ribosome

    The MITOCHONDRIA are the 'powerhouse of the cell' — they produce energy in the form of ATP through cellular respiration. ASVAB General Science tests basic biology. Other organelles: NUCLEUS (contains DNA, controls the cell); RIBOSOMES (make proteins); CELL MEMBRANE (controls what enters/exits); CHLO… Full explanation →

35. What is the chemical symbol for water?

    • O2
    • H2O ✓
    • NaCl
    • CO2

    WATER is H2O — two hydrogen atoms bonded to one oxygen atom. ASVAB General Science includes basic chemistry. Other common formulas: CO2 (carbon dioxide); O2 (oxygen gas); NaCl (sodium chloride/table salt); CH4 (methane). Knowing common chemical formulas and symbols (H = hydrogen, O = oxygen, C = car… Full explanation →

36. What is the basic unit of electrical resistance?

    • Watt
    • Ohm ✓
    • Ampere
    • Volt

    The OHM is the basic unit of electrical RESISTANCE. ASVAB General Science covers basic physics/electricity. Key electrical units: VOLT (voltage/electrical potential); AMPERE/amp (current); OHM (resistance); WATT (power). OHM'S LAW relates them: V = I × R (Voltage = Current × Resistance). Knowing whi… Full explanation →

37. What causes the tides in Earth's oceans?

    • Ocean currents only
    • Wind only
    • The gravitational pull of the Moon (and Sun) ✓
    • Earth's rotation only

    TIDES are caused primarily by the GRAVITATIONAL PULL of the MOON (and to a lesser extent the Sun) on Earth's oceans. ASVAB General Science includes earth science/astronomy. The Moon's gravity pulls ocean water toward it, creating high tides; there are generally two high and two low tides per day. SP… Full explanation →

38. On the pH scale, a substance with a pH of 7 is considered:

    • Basic (alkaline)
    • Radioactive
    • Neutral ✓
    • Acidic

    A pH of 7 is NEUTRAL (neither acidic nor basic) — pure water is neutral. ASVAB General Science includes the pH scale. The scale runs 0-14: BELOW 7 = ACIDIC (lower = more acidic, e.g., lemon juice, stomach acid); ABOVE 7 = BASIC/ALKALINE (higher = more basic, e.g., bleach, soap); EXACTLY 7 = NEUTRAL.… Full explanation →

39. Which of these is an example of a chemical change rather than a physical change?

    • Tearing a piece of paper
    • Wood burning into ash ✓
    • Boiling water into steam
    • Ice melting into water

    WOOD BURNING is a CHEMICAL CHANGE — it produces new substances (ash, gases) and cannot be reversed; the chemical composition changes. ASVAB General Science distinguishes physical vs chemical changes. PHYSICAL CHANGES (no new substance, often reversible): melting ice, boiling water, tearing paper, di… Full explanation →

40. Which blood cells are primarily responsible for fighting infection?

    • Plasma
    • White blood cells ✓
    • Red blood cells
    • Platelets

    WHITE BLOOD CELLS (leukocytes) are primarily responsible for FIGHTING INFECTION as part of the immune system. ASVAB General Science covers the circulatory/immune system. Blood components: RED BLOOD CELLS (carry oxygen via hemoglobin); WHITE BLOOD CELLS (fight infection/immunity); PLATELETS (help blo… Full explanation →

41. Which planet is closest to the Sun?

    • Mars
    • Mercury ✓
    • Earth
    • Venus

    MERCURY is the planet closest to the Sun. ASVAB General Science includes astronomy. The planets in order from the Sun: MERCURY, VENUS, EARTH, MARS, JUPITER, SATURN, URANUS, NEPTUNE (a common mnemonic: 'My Very Educated Mother Just Served Us Noodles'). Mercury is closest (and has extreme temperatures… Full explanation →

42. What is the term for the force that pulls objects toward the center of the Earth?

    • Gravity ✓
    • Inertia
    • Friction
    • Magnetism

    GRAVITY is the force that pulls objects toward the center of the Earth (and that attracts masses to each other generally). ASVAB General Science/physics covers basic forces. Near Earth's surface, gravity accelerates falling objects at about 9.8 m/s². Other concepts: FRICTION (resists motion between … Full explanation →

43. What process do plants use to convert sunlight, water, and carbon dioxide into food (glucose) and oxygen?

    • Digestion
    • Fermentation
    • Photosynthesis ✓
    • Respiration

    PHOTOSYNTHESIS is the process by which plants (using chlorophyll in chloroplasts) convert SUNLIGHT, WATER, and CARBON DIOXIDE into GLUCOSE (food/energy) and release OXYGEN. ASVAB General Science covers this key biological process. Equation concept: CO2 + H2O + light energy → glucose + O2. Photosynth… Full explanation →

44. What are the three most common states of matter?

    • Hot, warm, and cold
    • Hard, soft, and liquid
    • Solid, liquid, and gas ✓
    • Big, medium, and small

    The three most common states of matter are SOLID, LIQUID, and GAS. ASVAB General Science covers states of matter. SOLID (definite shape and volume — particles tightly packed); LIQUID (definite volume, takes the container's shape — particles flow); GAS (no definite shape or volume — particles spread … Full explanation →

45. What gas do humans need to breathe in to survive, and what gas do they exhale?

    • Inhale oxygen, exhale carbon dioxide ✓
    • Inhale carbon dioxide, exhale oxygen
    • Inhale hydrogen, exhale oxygen
    • Inhale nitrogen, exhale helium

    Humans INHALE OXYGEN (needed for cellular respiration to produce energy) and EXHALE CARBON DIOXIDE (a waste product of respiration). ASVAB General Science covers the respiratory system. In the lungs, oxygen from inhaled air passes into the blood, and carbon dioxide passes out of the blood to be exha… Full explanation →

46. What is the innermost layer of the Earth called?

    • Crust
    • Core ✓
    • Mantle
    • Atmosphere

    The CORE is the innermost layer of the Earth. ASVAB General Science includes earth science. Earth's layers from outside in: CRUST (thin outer layer where we live); MANTLE (thick middle layer of hot, semi-solid rock); CORE (innermost — divided into a liquid OUTER CORE and a solid INNER CORE, composed… Full explanation →

47. Sound travels fastest through which medium?

    • A gas
    • A vacuum
    • A solid ✓
    • Sound travels at the same speed everywhere

    Sound travels FASTEST through SOLIDS (then liquids, then gases — slowest in gases like air). ASVAB General Science/physics covers wave properties. Sound is a mechanical wave requiring a medium; it travels faster when particles are closer together (denser, more tightly bound), so: SOLID > LIQUID > GA… Full explanation →

48. What is the powerhouse of the cell, responsible for producing energy?

    • Cell membrane
    • Nucleus
    • Ribosome
    • Mitochondria ✓

    The mitochondria are often called the 'powerhouse of the cell' because they produce most of the cell's energy in the form of ATP through cellular respiration. The nucleus contains the cell's DNA and controls its activities; ribosomes build proteins; and the cell membrane controls what enters and lea… Full explanation →

49. Which process do plants use to convert sunlight, water, and carbon dioxide into glucose and oxygen?

    • Respiration
    • Photosynthesis ✓
    • Fermentation
    • Digestion

    Photosynthesis is the process by which plants (and some other organisms) use sunlight to convert carbon dioxide and water into glucose (sugar) and oxygen. It occurs mainly in the chloroplasts, which contain the green pigment chlorophyll that captures light energy. Respiration is almost the reverse p… Full explanation →

50. What is the smallest unit of an element that retains the properties of that element?

    • A cell
    • A molecule
    • An atom ✓
    • A compound

    An atom is the smallest unit of an element that still has the properties of that element. Atoms consist of protons and neutrons in a central nucleus, with electrons surrounding it. A molecule is two or more atoms bonded together (which may be the same element or a compound). A compound is a substanc… Full explanation →

51. On the pH scale, a substance with a pH of 3 is best described as:

    • A strong base
    • An acid ✓
    • Neutral
    • A salt

    The pH scale runs from 0 to 14. A pH below 7 is acidic, exactly 7 is neutral (like pure water), and above 7 is basic (alkaline). A pH of 3 is well below 7, so the substance is an acid (and a fairly strong one, since lower numbers mean more acidic). Examples of acids in the low pH range include lemon… Full explanation →

52. Which of Newton's laws states that for every action there is an equal and opposite reaction?

    • Newton's third law ✓
    • Newton's first law
    • The law of gravity
    • Newton's second law

    Newton's third law of motion states that for every action there is an equal and opposite reaction — when one object exerts a force on a second, the second exerts an equal force in the opposite direction on the first. A rocket pushing exhaust down and being pushed up is a classic example. Newton's fi… Full explanation →

53. What term describes the transfer of heat through direct contact between materials?

    • Radiation
    • Insulation
    • Conduction ✓
    • Convection

    Conduction is the transfer of heat through direct contact between materials, as when a metal spoon heats up in a hot pot of soup. Convection is heat transfer through the movement of fluids (liquids or gases), such as warm air rising. Radiation transfers heat through electromagnetic waves and needs n… Full explanation →

54. What causes the cycle of day and night on Earth?

    • Changes in the seasons
    • Earth's orbit around the Sun
    • Earth's rotation on its axis ✓
    • The Moon's gravity

    Day and night are caused by Earth's rotation on its axis, which takes about 24 hours. As Earth spins, the side facing the Sun experiences day and the side facing away experiences night. Earth's orbit around the Sun (about 365 days) causes the year and, combined with the tilt of the axis, the seasons… Full explanation →

55. Which layer of Earth is the thin, solid outer layer on which we live?

    • The mantle
    • The atmosphere
    • The core
    • The crust ✓

    Earth's crust is the thin, solid outermost layer where we live; it includes both continents and the ocean floor. Beneath it lies the mantle, a thick layer of hot, semi-solid rock that slowly flows, and below that the core (a liquid outer core and a solid inner core, composed largely of iron and nick… Full explanation →

56. Which body system is primarily responsible for transporting oxygen and nutrients to cells throughout the body?

    • The circulatory system ✓
    • The respiratory system
    • The digestive system
    • The nervous system

    The circulatory (cardiovascular) system — the heart, blood, and blood vessels — transports oxygen, nutrients, hormones, and waste products throughout the body. The respiratory system (lungs) brings oxygen into the blood and removes carbon dioxide, but the circulatory system does the actual delivery … Full explanation →

57. What does the chemical formula H₂O represent, and what do the symbols mean?

    • Oxygen gas
    • Two hydrogen atoms only
    • Water — two hydrogen atoms bonded to one oxygen atom ✓
    • Hydrogen peroxide

    H₂O is the chemical formula for water. The subscript 2 after H means there are two hydrogen atoms, and the O (with an implied subscript of 1) means one oxygen atom, so each water molecule is two hydrogen atoms bonded to one oxygen atom. Hydrogen peroxide is a different compound, H₂O₂ (two hydrogens … Full explanation →

58. What molecule carries the genetic instructions for living organisms?

    • Protein
    • Glucose
    • DNA ✓
    • Water

    DNA (deoxyribonucleic acid) carries the genetic instructions that determine an organism's traits and guide the building of proteins. It is found in the nucleus of cells and is organized into structures called chromosomes. DNA's famous double-helix shape stores information in sequences of four bases.… Full explanation →

59. What is the basic unit used to measure electric current?

    • Watt
    • Volt
    • Ohm
    • Ampere (amp) ✓

    Electric current — the flow of electric charge — is measured in amperes, often shortened to amps (symbol A). The volt is the unit of electric potential difference (voltage), the ohm is the unit of electrical resistance, and the watt is the unit of power. These quantities are related by Ohm's law and… Full explanation →

60. Which planet is the largest in our solar system?

    • Earth
    • Mars
    • Jupiter ✓
    • Saturn

    Jupiter is the largest planet in our solar system — a gas giant whose mass is greater than all the other planets combined. Saturn is the second largest and is famous for its prominent rings. Earth and Mars are far smaller, rocky (terrestrial) planets. Basic astronomy facts like the order and relativ… Full explanation →

61. Which part of the human body produces insulin to regulate blood sugar?

    • The stomach
    • The pancreas ✓
    • The liver
    • The kidneys

    The pancreas produces insulin, a hormone that regulates the level of glucose (sugar) in the blood by helping cells absorb it. When insulin production or function is impaired, the result can be diabetes. The liver stores and releases glucose and performs many other functions but does not make insulin… Full explanation →