Question

A radioactive material has an initial amount 16 gm. After 120 days it reduces to 1 gm, then the half-life of radioactive material is.

• A. 60 days
• B. 30 days
• C. 40 days
• D. 240 days

Answer 1

Answer: (B)

30 days

Answer 2

$\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{n} \Rightarrow \left( \frac{1}{16} \right) = \left( \frac{1}{2} \right)^{n} \Rightarrow n = 4$

also $n = \frac{t}{T_{1/2}} \Rightarrow T_{1/2} = \frac{120}{4} = 30\mspace{6mu} days$