Home / AP Physics 2: 7.2 Radioactive Decay – Exam Style questions with Answer- MCQ

AP Physics 2: 7.2 Radioactive Decay – Exam Style questions with Answer- MCQ

Question

How many neutrons are contained in the isotope \(_{92}^{238}U\)?
(A) 92
(B) 100
(C) 146
(D) 330

▶️Answer/Explanation

Ans:(C)

238 nucleons − 92 protons = 146 neutrons

Question

In the reaction below, what is the mass number for particle X? 
                        \(^{27}_{13}Al+^{4}_{2}He\rightarrow ^{30}_{15}P+X\)
(A) 1
(B) 2
(C) 0
(D) − 1

▶️Answer/Explanation

Ans:(A)

The total mass number (upper number) on each side of the reaction must be equal.

Question

Radon gas \((^{222}_{86}Rn)\) is radioactive with a half-life of 4 days as it undergoes alpha decay. A sample is sealed in an evacuated tube for more than 1 week. At that time, the presence of a second gas is detected. This gas is most probably
(A) hydrogen
(B) helium
(C) nitrogen
(D) argon

▶️Answer/Explanation

Ans:(B)

Radon undergoes alpha decay. Since alpha particles are the nuclei of helium, the new gas is most likely helium because these alpha particles have picked up some electrons.

Question

According to the scale of binding energy per nucleon, which atom has the most stable nuclear isotope?
(A) Hydrogen because it cannot decay into anything
(B) Hydrogen because it can exist with only one nucleon
(C) Iron because its nucleons are the most tightly bound
(D) Iron because it is in the middle of the periodic table

▶️Answer/Explanation

Ans:(C)

Iron has the most stable nucleus since it has the greatest binding energy per nucleon of all the nuclei. Fusion of lighter elements stop being energy producing when they fuse up to Fe. Fission of heavier elements stop being energy releasing after fissioning down to Fe.

Question

What is the function of a moderator in a fission reactor?
(A) Control the number of neutrons
(B) Act as a source of fissionable material
(C) Control the costs of running the reactor
(D) Control the half-life of the radioactive material

▶️Answer/Explanation

Ans:(A)

The moderator absorbs neutrons to manage the rate at which the chain reaction propagates.

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