Question

Initial mass of ${}_{84}P{o}^{218}$ is 1 gram. After what time 0.875 gram of it will be disintegrated ? $(T_{1/2}=3minutes)$

• A. $12$ minutes
• B. $6$ minutes
• C. Infinity
• D. $9$ minutes

Answer 1

The correct option is D $9$ minutes

Initial mass $M_o=1gm$

Mass remained $M=1-0.875=0.125gm$

Using $M=\frac{M_o}{2^n}$

Or $0.125=\frac{1}{2^n}$

Or $2^n=8=2^3$

$⟹n=3$

Or time $t=n\times T_{1/2}=3\times 3=9minutes$