Physics Nuclear Physics MDCAT 2017
PMDC Verified Question 61 of 98
The half-life of radium is about 1600 years. If 100 g radium existing now, 25 g will remain un-decayed after:
A
4800 years
B
2400 years
C
6400 years
D
3200 years
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 3200 years


Concept:

Determine how many successive divisions by 2 are required to reduce the initial mass to the final mass, then multiply by the half-life duration.

Solution:

  • Initial mass = 100 g. Target mass = 25 g.


  • Track the decay:
    100 g \(\rightarrow\) 50 g (1 half-life)
    50 g \(\rightarrow\) 25 g (2 half-lives).


  • Therefore, exactly 2 half-lives have elapsed.


  • Total time = \(n \times T_{1/2} = 2 \times 1600\text{ years} = 3200\text{ years}\).


Why other options are incorrect:

Option A (4800) is 3 half-lives (leaving 12.5g). Option C (6400) is 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.

Previous Question All Nuclear Physics MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App