MHT CET20255 May 2025Evening ShiftPhysicsNuclear PhysicsActual
A radioactive element having half-life 30 min . is undergoing beta decay. The fraction of radioactive element remains undecayed after 90 min . will be
Options
- A1 2
- B1 4
- C1 8
- D1 16
Correct answer
C. 1 8
Step-by-step solution
The fraction of radioactive material remaining after time t is determined by the decay formula: N N₀ = ( 1 2 )^ t/T_ 1/2 Given a half-life T_ 1/2 = 30 min and time t = 90 min , the elapsed time spans 3 half-lives. Substituting into the decay law yields: N N₀ = ( 1 2 )^3 = 1 8 The fraction remaining undecayed is therefore 1 8 .