JEE Main 2021 · PhysicsMultiple choiceSingle correctEasyCalculation

JEE Main 3 August 2021, Shift 2, Physics Q18

Question 18 of 90 in this shift, Physics question 18 of 30, Section A.

A radioactive isotope has a half life of T years. After how much time is its activity reduced to 6.25% of its original activity ?

(1)2 T years
(2)4 T yearsOfficial answer
(3)1.5 T years
(4)1 T year

Official answer

Option 2

NTA final key.

Chapter: Nuclei
Topic: Radioactive Decay
Idea tested: Half-Life Calculations

Same idea in other shifts

Asked 5× 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 42 of the 174 JEE Main shifts held from 2017 to 2026.