General Science Practice Test 5 (ASVAB)

Answer: A

Correct answer: Number of neutrons. The atomic number, 6 protons, identifies carbon, so both isotopes share it. The numbers 12 and 14 are mass numbers, and the difference comes from carbon-14 having 2 more neutrons.

• A (correct): Isotopes of one element have the same protons but different neutron counts, which changes their mass.
• B: Every carbon atom has 6 protons; changing the proton count would make a different element.
• C: A neutral atom has as many electrons as protons, so both neutral isotopes have 6 electrons.
• D: The atomic number is the proton count, which is 6 for all carbon atoms.

Answer: D

Correct answer: Convection. When air is heated, it expands and becomes less dense, so cooler, denser air sinks and pushes it upward. This circulation, called a convection current, carries thermal energy through the room along with the moving air itself. Convection happens only in fluids, meaning liquids and gases. Conduction is the common mix-up, but it passes energy from particle to particle without the material flowing, as along a metal pan handle.

• A: Reflection changes the direction of waves and does not explain rising warm air.
• B: Conduction transfers thermal energy through microscopic interactions, not the described moving air.
• C: Freezing is a phase change from liquid to solid, not the movement of warm air.
• D (correct): Convection describes bulk motion of a fluid such as heated air that transports thermal energy.

Answer: C

Correct answer: Kidney. Each kidney contains about a million nephrons that filter blood plasma, then reabsorb useful substances such as water, glucose and salts and secrete wastes into the filtrate. What remains becomes urine. The kidneys therefore control both waste removal and the body's water and salt balance. The bladder is a tempting choice because urine collects there, but it only stores urine; the ureters and urethra simply carry it.

• A: A ureter transports urine from kidney to bladder.
• B: The bladder stores urine made elsewhere.
• C (correct): Kidneys filter and adjust fluid composition before urine leaves through ureters.
• D: The pancreas produces digestive secretions and endocrine hormones.

Answer: D

Correct answer: The height the ball is dropped from. The independent variable is the factor the experimenter deliberately changes. Here the student picks the drop heights of 50, 100 and 150 cm, so drop height is the independent variable.

• A: The landing surface should stay the same throughout, so it is a controlled variable.
• B: Bounce height is the outcome being measured, which makes it the dependent variable.
• C: The same ball is used every time, so ball type is a controlled variable.
• D (correct): The student chooses and changes the drop height on purpose, so it is the independent variable.

Answer: B

Correct answer: A convergent boundary, with earthquakes, volcanoes and possible tsunamis. When an oceanic plate sinks beneath another plate, the plates are moving together, which is a convergent boundary called a subduction zone. These zones produce volcanoes, deep trenches, strong earthquakes and possible tsunamis.

• A: At divergent boundaries plates separate, as at mid-ocean ridges; here one plate is sinking under another.
• B (correct): Plates colliding with one sinking below the other is a subduction zone, which builds volcanoes and produces large earthquakes and tsunamis.
• C: Transform boundaries have plates sliding sideways, not one plate diving beneath the other.
• D: Colliding plates store and release great strain, so subduction zones are among the most earthquake-prone places on Earth.

Answer: C

Correct answer: 30 m. Displacement equals the area between a velocity graph and the time axis. Here the region is a triangle.

• A: This is the slope of the line, which gives the acceleration in m/s², not the displacement.
• B: This treats the area as a full rectangle, as if the object moved at 6 m/s the whole time.
• C (correct): The area under the line is a triangle: one half times 10 s times 6 m/s equals 30 m.
• D: This reads the height of the line as a position; the height is the velocity at the end.

Answer: B

Correct answer: 12. Protons carry a +1 charge and electrons a −1 charge of exactly equal size, so an atom is neutral only when the two counts match. The proton count, or atomic number, is fixed for an element (12 means magnesium), but electrons can be gained or lost to form ions. A common slip is to bring neutrons into it; neutrons are uncharged, so they never affect the electron count of a neutral atom.

• A: Twenty-four would make a strongly negative ion.
• B (correct): Neutrality requires as many electrons as protons.
• C: Ten would leave a +2 charge.
• D: Six would leave a +6 charge if protons were twelve.

Answer: C

Correct answer: It releases only a small fraction of its hydrogen ions in water. Acid strength is how completely the acid ionizes in water. A strong acid releases nearly all of its hydrogen ions, while a weak acid, such as acetic acid, releases only a small fraction. How much water is present is a separate idea, concentration.

• A: Any acid solution has a pH below 7; a pH above 7 is basic.
• B: That describes a dilute solution, which is about concentration, not strength.
• C (correct): Strength describes how completely an acid ionizes, and a weak acid ionizes only partly.
• D: Weak acids such as vinegar still react with and neutralize bases, forming a salt and water.

Answer: C

Correct answer: It increases reaction rate by lowering activation energy. Every reaction must clear an energy barrier, the activation energy, before reactants can become products. An enzyme binds its substrate at the active site and positions it so the barrier is lower, letting the reaction happen much faster at body temperature. The enzyme leaves unchanged and can be used again. Enzymes speed up reactions that are already possible but cannot make an impossible reaction happen or create energy, and they are not fuel that gets used up.

• A: Catalysts do not remove the need for reactants and favorable energy conditions.
• B: An enzyme is not ordinarily used up as its reaction proceeds.
• C (correct): Correct: Enzymes act as catalysts and lower activation energy without being consumed in the overall reaction.
• D: Enzymes do not create energy from nothing.

Answer: A

Correct answer: Tendon. Muscles can only pull, and the tendon is the dense, cord-like connective tissue that delivers that pull to a bone so a joint moves. The Achilles tendon, which connects the calf muscles to the heel bone, is a familiar example. The ligament is the tempting wrong answer because it is made of similar tough tissue, but ligaments connect bone to bone. A memory hook: tendons tie muscle to bone, while ligaments link bone to bone.

• A (correct): A tendon transfers muscle force to bone for movement.
• B: A ligament joins bones and stabilizes joints.
• C: A neuron is a signaling cell rather than a connective band.
• D: Cartilage cushions or supports tissue but is not the typical muscle-to-bone cord.

Answer: D

Correct answer: A 90 g object with a volume of 120 cm³. An object floats if its density is less than the fluid's. Dividing mass by volume gives 1.2, 0.75, 1.2 and 1.5 g/cm³. Only the 0.75 g/cm³ object is less dense than water, so only it floats.

• A: Its density is 300 ÷ 250 = 1.2 g/cm³, so it sinks even though its volume is large.
• B: Its density is 60 ÷ 50 = 1.2 g/cm³, greater than water, so it sinks.
• C: Its density is 45 ÷ 30 = 1.5 g/cm³, so it sinks even though it is the lightest object.
• D (correct): Its density is 90 ÷ 120 = 0.75 g/cm³, less than water, so it floats.

Answer: C

Correct answer: Incorrect: dominance describes heterozygote phenotype, not fitness or frequency. Dominance only tells you which allele's trait shows when an individual carries one copy of each. Whether an allele becomes common depends on selection, mutation, migration and chance events such as genetic drift. Huntington disease is caused by a dominant allele yet is rare and harmful, while many recessive alleles are common. The tempting belief that dominant means stronger or more widespread confuses how a trait is expressed with how well it helps survival and reproduction.

• A: Dominance does not establish harm either; many dominant alleles are neutral or beneficial.
• B: Autosomal or sex-chromosome location does not turn dominance into evidence of fitness.
• C (correct): Dominance tells which allele's trait shows in a heterozygote; it says nothing about survival advantage or how common the allele is.
• D: Dominance does not guarantee higher reproductive success, so a dominant allele need not spread.

Answer: D

Correct answer: 45 seconds. Count up from the earlier time rather than subtracting digits directly: from 10:03:20 to 10:04:00 is 40 seconds, then 5 more seconds reaches 10:04:05. Because P waves travel faster than S waves, the gap between their arrivals grows with distance, so seismologists use this S–P interval to estimate how far away an earthquake occurred. A common slip is treating a minute as 100 seconds when borrowing.

• A: 25 seconds undercounts the gap; 10:03:20 to 10:04:00 alone is already 40 seconds.
• B: 85 seconds comes from subtracting 320 from 405 as plain numbers, treating a minute as 100 seconds.
• C: 35 seconds miscounts the 40 seconds from 10:03:20 to 10:04:00 before adding the final 5 seconds.
• D (correct): Subtract 10:03:20 from 10:04:05: 40 seconds to 10:04:00 plus 5 seconds = 45 seconds.

Answer: A

Correct answer: 24 years since emission. A light-year is a distance, not a time: it is how far light travels in one year, about 9.5 trillion km. So a star 24 light-years away sends light that needs 24 years to reach us, and we see the star as it was 24 years ago. The tempting error is reading light-year as a unit of time or mixing it up with light-hours. Looking at distant objects is always looking into the past.

• A (correct): Light took about 24 years to cover 24 light-years.
• B: One month is not the travel time for 24 light-years.
• C: A millionfold factor is not given or justified.
• D: Light-year does not mean light-hour.

Answer: B

Correct answer: An aquatic biomass pyramid can be inverted even if its energy pyramid is upright. A biomass pyramid shows how much living material exists at one moment, while an energy pyramid shows energy produced over time. Phytoplankton reproduce very quickly and are eaten almost as fast, so their standing mass can be smaller than that of the zooplankton feeding on them. Over a year, however, they still produce far more energy than the zooplankton receive. The misconception is assuming biomass and energy pyramids must have the same shape.

• A: Energy declines at each transfer, so an energy pyramid stays upright even when biomass is inverted.
• B (correct): High producer turnover can permit low standing producer biomass with greater consumer biomass.
• C: Algae remain producers because they photosynthesize, regardless of how much biomass is present at one moment.
• D: Aquatic organisms use trophic transfers.