Physics Nuclear Physics MDCAT 2015
PMDC Verified Question 70 of 98
According to the equation $$ _{Z}^{A}\text{X} \rightarrow \text{Y} + 3\alpha \text{ particles} $$, what are the atomic and mass numbers of 'Y'?
A
Z-6, A-12
B
Z+1, A
C
Z-2, A-4
D
Z+3, A
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Z-6, A-12


Concept:

The principle of conservation of nucleon number and charge number dictates that the sums of \(A\) and \(Z\) on both sides of a nuclear equation must be perfectly equal.

Solution:

  • The decay emits 3 alpha particles. One alpha particle is \(_{2}^{4}\text{He}\).


  • Total mass number removed by 3 alphas: \(3 \times 4 = 12\).


  • Total atomic number removed by 3 alphas: \(3 \times 2 = 6\).


  • Set up the conservation equation: $$ _{Z}^{A}\text{X} \rightarrow _{Z_Y}^{A_Y}\text{Y} + 3 \, (_{2}^{4}\text{He}) $$


  • Solve for Y: $$ A_Y = A - 12 $$ $$ Z_Y = Z - 6 $$


Why other options are incorrect:

Option C is the result for only 1 alpha particle. Options B and D describe beta or other physically incorrect decay paths.

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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