Physics Nuclear Physics MDCAT 2014
PMDC Verified Question 76 of 98
A naturally occurring radioactive element decays two alpha particles. Which one of the following represents the status of daughter element with respect to mass number A and charge number Z?
A
Z decreases by 4 and A decreases by 2
B
Z decreases by 4 and A decreases by 8
C
Z decreases by 2 and A decreases by 4
D
Z decreases by 8 and A decreases by 4
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Z decreases by 4 and A decreases by 8


Concept:

Each individual alpha particle (\(_{2}^{4}\text{He}\)) carries away 2 protons and 4 total nucleons.

Solution:

  • For two alpha particles emitted simultaneously or sequentially, the total loss must be multiplied by 2.


  • Change in Charge Number (\(Z\)): $$ \Delta Z = 2 \times (-2) = -4 $$


  • Change in Mass Number (\(A\)): $$ \Delta A = 2 \times (-4) = -8 $$


Why other options are incorrect:

Option C is the result for only one alpha particle. Option A perfectly reverses the changes of Z and A for a single particle. Option D reverses Z and A for two particles.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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