Question

The decay constant of a radioactive element is defined as the reciprocal of the time interval after which the number of atoms of the radioactive element falls to nearly

• A. $50\%$ of its original number
• B. $36.8\%$ of its original number
• C. $63.2\%$ of its original number
• D. $75\%$ of its original number

Answer 1

The correct option is B $36.8\%$ of its original number

Definition of decay constant is as follows, $\text{Decay constant is the reciprocal of time duration in which the element falls to 1/e or 36.8\% of its initial amount}$

If we use $N=N_0{e}^{-\lambda t}$ and put $N=N_0/e$ we will get decay constant $\lambda =1/t$

Option B is correct.