Question

The half life of radium is $1600$ years. The time $1gm$ of radium take to reduce to $0.125gm$ is:

• A. $4800years$
• B. $4500years$
• C. $5000years$
• D. $4750years$

Answer 1

Answer: (A)

$4800years$

The ratio of radium left $=\frac{0.125}{1}$$=\frac{1}{8}$$=(\frac{1}{2}{)}^3$

i.e. after 3 half lives, it became $(\frac{1}{8}{)}^{th}$ of the initial amount.

$t_{1/2}=1600yrs$

$3t_{1/2}=4800yrs$