Question

The half-life of radon is 3.8 days. Three forth of a radon sample decay in.

• A. 5.02 days
• B. 15.2 days
• C. 7.6 days
• D. 11.4 days

Answer 1

Answer: (C)

7.6 days

Answer 2

Decayed fraction $= \frac{3}{4}$, so undecayed fraction $= \frac{1}{4}$

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

⇒ $t = n \times T_{1/2} = 2 \times 3.8 = 7.6\mspace{6mu} days$