What percentage of original radioactive atoms is left after five half lives 
(a) 0.3%                (b) 1%
(c) 31%                  (d) 3.125%

(d) Fraction of atoms remains after five half lives
NN0=12t/T=125T/T=132
Percentage atom remains = 132×100=3.125%

Difficulty Level:

  • 18%
  • 14%
  • 14%
  • 57%