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Saturday, 31 October

JEE Main 2022 · PhysicsMultiple choiceSingle correctEasyCalculation

JEE Main 28 July 2022, Shift 1, Physics Q48

Question 48 of 90 in this shift, Physics question 18 of 30, Section A.

The half life period of a radioactive substance is 60 days. The time taken for 78\frac{7}{8}th of its original mass to disintegrate will be :
  1. (1)120 days
  2. (2)130 days
  3. (3)180 daysOfficial answer
  4. (4)20 days

Official answer

Option 3

NTA final key (2022 Session 2).

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

Same idea in other shifts

Asked 7× in all
  1. 27 Jul 2022, Shift 1 · Q48What is the half-life period of a radioactive material if its activity drops to 1/16th^{th} of its initial value in 30 years?EasySingle correct
  2. 28 Jul 2022, Shift 1 · Q52A freshly prepared radioactive source of half life 2 hours 30 minutes emits radiation which is 64 times the permissible safe level. The…EasyNumerical value
  3. 28 Jul 2022, Shift 2 · Q18A radioactive sample decays 78\frac{7}{8} times its original quantity in 15 minutes. The half-life of the sample isEasySingle correct
  4. 24 Jun 2022, Shift 2 · Q56A sample contains 10−210^{-2} kg each of two substances A and B with half lives 4 s and 8 s respectively. The ratio of their atomic weights…MediumNumerical value
  5. 25 Feb 2021, Shift 1 · Q19Two radioactive substances X and Y originally have N1N_1 and N2N_2 nuclei respectively. Half life of X is half of the half life of Y.…MediumSingle correct
  6. 25 Jul 2021, Shift 2 · Q27The nuclear activity of a radioactive element becomes (18)th\left(\frac{1}{8}\right)^{\text{th}} of its initial value in 30 years. The…EasyNumerical value

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.