If a radioactive element having half-life of 30 min is undergoing beta decay, the fraction of radioactive element remains undecayed after 90 min will be :

Step-by-step solution

Given: Half life of radioactive element t 1 2 = 30   min . In 90   min , there will be three half lives, so n = 3 . Using radioactive decay law, fraction of radioactive element remains undecayed is N N 0 = 1 2 n = 1 2 3 ⇒ N N 0 = 1 8