JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 25 February 2021, Shift 1, Physics Q19

Question 19 of 90 in this shift, Physics question 19 of 30, Section A.

Two radioactive substances X and Y originally have

N_1

and

N_2

nuclei respectively. Half life of X is half of the half life of Y. After three half lives of Y, number of nuclei of both are equal. The ratio

\frac{N_1}{N_2}

will be equal to :

(1) $\frac{3}{1}$
(2) $\frac{1}{3}$
(3) $\frac{8}{1}$ Official answer
(4) $\frac{1}{8}$

Official answer

Option 3

NTA final key.

Chapter: Nuclei
Topic: Radioactive Decay
Idea tested: Integer Half-Life Shortcuts

Same idea in other shifts

Asked 7× in all

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Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.