Question

The half life of polonium is 140 days. In what time will 15 g of polonium be disintegrated out of its initial mass of 16 g?

• A. 230 days
• B. 560 days
• C. 730 days
• D. 160 days

Answer 1

Answer: (B)

560 days

Answer 2

:here $m_{0} = 16g,m = 16 - 15 = 1g$

As $\frac{m}{m_{0}} = \left( \frac{1}{2} \right)^{n}or\frac{1}{16} = \left( \frac{1}{2} \right)^{4} = \left( \frac{1}{2} \right)^{n}$

$\Rightarrow n = 4$

Time taken to disintegrate=

$T_{12} \times n = 140 \times 4 = 560days$