Physics Nuclear Physics MDCAT 2017
PMDC Verified Question 60 of 98
The quantity of uranium is 400g. After \(3^{\text{rd}}\) half-life, how much uranium will be left?
A
50g
B
100g
C
25g
D
200g
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: 50g


Concept:

A half-life is the specific period it takes for exactly 50% of the radioactive atoms in a sample to decay.

Formula:

$$ N = N_0 \left(\frac{1}{2}\right)^n $$

Solution:

  • Initial quantity \(N_0 = 400\text{ g}\).


  • We can track the mass sequentially across \(n=3\) half-lives:


  • After 1st half-life: \(400 / 2 = 200\text{ g}\) left.


  • After 2nd half-life: \(200 / 2 = 100\text{ g}\) left.


  • After 3rd half-life: \(100 / 2 = 50\text{ g}\) left.


Why other options are incorrect:

200g remains after 1 half-life. 100g remains after 2 half-lives. 25g remains after 4 half-lives.

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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