Question

A radioactive sample has half-life of 5 years. Probability of decay in 10 years will be.

• A. 100%
• B. 75%
• C. 50%
• D. 25%

Answer 1

Answer: (B)

75%

Answer 2

Number of half lives $n = \frac{10}{5} = 2,$ now $\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{2} = \frac{1}{4}$

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

⇒ In percentage $= \frac{3}{4} \times 100 = 75\%$.