Question

Radon (Ra) decays into Polonium ($P_{0}$) by emitting an $\alpha -$particle with half-life of 4 days. A sample contains $6.4 \times 10^{10}$atoms of$Rn$. After 12 days, the number of atoms of $R_{n}$left in the sample will be.

• A. $3.2 \times 10^{10}$
• B. $0.53 \times 10^{10}$
• C. $2.1 \times 10^{10}$
• D. $0.8 \times 10^{10}$

Answer 1

Answer: (D)

$0.8 \times 10^{10}$

Answer 2

In the given case, 12 days = 3 half lives Number of atoms left after 3 half lives.

$= 6.4 \times 10^{10} \times \frac{1}{2^{3}} = 0.8 \times 10^{10}$