Question

What fraction of a radioactive material will get disintegrated in a period of two half-lives.

• A. Whole
• B. Half
• C. One-fourth
• D. Three-fourth

Answer 1

Answer: (D)

Three-fourth

Answer 2

$\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{n},\mspace{6mu} n = 2 \Rightarrow \frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{2} = \frac{1}{4}$

So disintegrated part

$= 1 - \frac{N}{N_{0}} = 1 - \frac{1}{4} = \frac{3}{4}$.