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Saturday, 31 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 idea in other shifts

Asked 3× in all
  1. 26 Aug 2021, Shift 2 · Q6At time t=0t=0, a material is composed of two radioactive atoms A and B, where NA(0)=2NB(0)\mathrm{N_A(0)=2N_B(0)}. The decay constant of both kind…HardDiagram basedHas a figure
  2. 31 Aug 2021, Shift 1 · Q3A sample of a radioactive nucleus A disintegrates to another radioactive nucleus B, which in turn disintegrates to some other stable…MediumDiagram basedHas a figure

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 108 of the 174 JEE Main shifts held from 2017 to 2026.