Learn

Friday, 9 October

JEE Main 2025 · PhysicsMultiple choiceDiagram basedMediumData or graph

JEE Main 4 April 2025, Shift 2, Physics Q42

Question 42 of 75 in this shift, Physics question 17 of 25, Section A.

A radioactive material P first decays into Q and then Q decays to non-radioactive material R. Which of the following figure represents time dependent mass of P, Q and R ?

The figure, in words

Four mass-vs-time graphs for P, Q and R, given as the options.
  1. (1)[figure: graph of mass vs time; P decreases monotonically; Q rises to a peak then falls; R rises slowly and later saturates/increases]Official answer
  2. (2)[figure: graph of mass vs time; P decreases; Q and R both increase steeply, Q curve above R]
  3. (3)[figure: graph of mass vs time; P decreases; Q rises to a high plateau; R rises to a lower plateau]
  4. (4)[figure: graph of mass vs time; P decreases fast; R rises to a peak then falls; Q increases steeply at later times]

Official answer

Option 1

NTA final key.

Chapter
Nuclei
Topic
Radioactive Decay
Idea tested
Successive Decay Chains

Same topic in other shifts

All Radioactive Decay questions
  1. 8 Apr 2026, Shift 2 · Q44Two radioactive substances A and B of mass numbers 200 and 212 respectively, shows spontaneous α\alpha-decay with same QQ value of 1…MediumSingle correct
  2. 8 Apr 2023, Shift 2 · Q44A radio active material is reduced to 1/8 of its original amount in 3 days. If 8×10−38\times10^{-3} kg of the material is left after 5 days…MediumSingle correct
  3. 11 Apr 2023, Shift 1 · Q33Two radioactive elements A and B initially have same number of atoms. The half life of A is same as the average life of B. If λA\lambda_A…EasySingle correct
  4. 28 Jul 2022, Shift 1 · Q48The 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…EasySingle correct
  5. 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
  6. 29 Jun 2022, Shift 1 · Q33The activity of a radioactive material is 2.56×10−32.56 \times 10^{-3} Ci. If the half life of the material is 5 days, after how many days the…EasySingle correct

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. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.