58. why are tracers used in medicine?
a. to block radiation
b. to track organs
c. to cool reactions
d. to destroy bacteria
59. nuclear energy is powerful because —
a. it uses weak bonds
b. it uses chemical heat
c. it releases nucleus energy
d. it uses valence electrons
60. what stops gamma radiation best?
a. paper
b. plastic
c. aluminum
d. concrete
physical vs chemical changes & reactions
(61–80)
61. which is a chemical change?
a. melting ice
b. tearing paper
c. rusting iron
d. crushing a can
62. which is a physical change?
a. burning wood
b. cooking eggs
c. evaporating water
d. digesting food
63. which indicates a chemical reaction occurred?
a. shape change
b. temperature change
c. phase change
d. size change
64. which is evidence of a gas forming?
a. color change
b. solid forming
c. bubbles
d. odor
65. which reaction absorbs heat?
a. exothermic
b. endothermic
c. nuclear
d. combustion
66. which reaction releases heat?
a. endothermic
b. exothermic
c. nuclear
d. physical
67. what law requires equations to be balanced?
a. law of gravity
b. conservation of mass
c. newton’s first law
d. law of inertia
68. reactants are found on which side of an equation?
a. right
b. left
c. both
d. bottom
69. what does the arrow (→) mean?
a. plus
b. equals
c. yields
d. reacts
70. a solid forming in a liquid is called —
a. gas
b. precipitate
c. solution
d. residue
71. what type of reaction forms a compound?
a. decomposition
b. synthesis
c. replacement
d. combustion
72. what type of reaction breaks down a compound?
a. decomposition
b. synthesis
c. replacement
d. neutralization

Question

Accepted Answer

### Question 58: Why are tracers used in medicine?
# Brief Explanations:
Tracers in medicine are used to track the function or movement of organs/body parts. Option A is incorrect as tracers don't block radiation. Option C is wrong as they don't cool reactions. Option D is incorrect as they aren't for destroying bacteria. So the correct answer is to track organs.
# Answer:
B. To track organs

### Question 59: Nuclear energy is powerful because —
# Brief Explanations:
Nuclear energy comes from the energy released from the nucleus (nuclear fission/fusion). Option A is wrong (nuclear uses strong nuclear force, not weak bonds). Option B is incorrect (it's not chemical heat). Option D is wrong (valence electrons are for chemical, not nuclear, reactions). So it releases nucleus energy.
# Answer:
C. It releases nucleus energy

### Question 60: What stops gamma radiation best?
# Brief Explanations:
Gamma radiation is highly penetrating. Concrete (or thick lead) is effective. Paper, plastic, and aluminum are not effective against gamma. So concrete stops it best.
# Answer:
D. Concrete

### Question 61: Which is a chemical change?
# Brief Explanations:
Chemical change involves new substance formation. Melting ice (A) is physical (state change). Tearing paper (B) is physical (shape). Crushing a can (D) is physical. Rusting iron (C) forms iron oxide, a new substance, so it's chemical.
# Answer:
C. Rusting iron

### Question 62: Which is a physical change?
# Brief Explanations:
Physical change doesn't form new substances. Burning wood (A) is chemical (new substances). Cooking eggs (B) is chemical (protein denaturation). Digesting food (D) is chemical. Evaporating water (C) is state change (liquid to gas), no new substance, so physical.
# Answer:
C. Evaporating water

### Question 63: Which indicates a chemical reaction occurred?
# Brief Explanations:
Chemical reactions often show temperature change (energy change), new substance. Shape (A), phase (C), size (D) changes can be physical. Temperature change (B) can indicate energy release/absorption in a chemical reaction.
# Answer:
B. Temperature change

### Question 64: Which is evidence of a gas forming?
# Brief Explanations:
Bubbles are gas escaping. Color change (A) can be chemical but not gas. Solid forming (B) is precipitate. Odor (D) is a sign but not gas formation. So bubbles indicate gas.
# Answer:
C. Bubbles

### Question 65: Which reaction absorbs heat?
# Brief Explanations:
Endothermic reactions absorb heat. Exothermic (A) releases. Nuclear (C) and combustion (D) are exothermic (combustion releases heat). So endothermic absorbs.
# Answer:
B. Endothermic

### Question 66: Which reaction releases heat?
# Brief Explanations:
Exothermic reactions release heat. Endothermic (A) absorbs. Nuclear (C) can be exothermic but combustion is exothermic, but exothermic is the type that releases. So exothermic releases heat.
# Answer:
B. Exothermic

### Question 67: What law requires equations to be balanced?
# Brief Explanations:
Conservation of mass states matter is neither created nor destroyed, so chemical equations must be balanced. Law of gravity (A) is about gravity. Newton's First Law (C, Law of Inertia) is about motion. So conservation of mass.
# Answer:
B. Conservation of mass

### Question 68: Reactants are found on which side of an equation?
# Brief Explanations:
In a chemical equation, reactants (what you start with) are on the left, products on the right. So reactants are on the left.
# Answer:
B. Left

### Question 69: What does the arrow (→) mean?
# Brief Explanations:
In a chemical equation, the arrow means "yields" (produces). It's not plus (A), equals (B), or reacts (D). So it means yields.
# Answer:
C. Yields

### Question 70: A solid forming in a liquid is called —
# Brief Explanations:
A solid forming from a liquid (solution) is a precipitate. Gas (A) is not solid. Solution (C) is homogeneous. Residue (D) is solid left after evaporation, but precipitate is solid from reaction in liquid.
# Answer:
B. precipitate

### Question 71: What type of reaction forms a compound?
# Brief Explanations:
Synthesis reaction is combining substances to form a compound (A + B → AB). Decomposition (A) breaks down. Replacement (C) replaces. Combustion (D) is a type of reaction but not for forming compounds generally. So synthesis.
# Answer:
B. Synthesis

### Question 72: What type of reaction breaks down a compound?
# Brief Explanations:
Decomposition reaction breaks down a compound into simpler substances (AB → A + B). Synthesis (B) builds. Replacement (C) replaces. Neutralization (D) is acid - base. So decomposition.
# Answer:
A. Decomposition

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Question 58: Why are tracers used in medicine?

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Question 59: Nuclear energy is powerful because —