Question

Activity of a radioactive substance becomes from $8000Bq$ to $1000Bq$ in $12$ days. What is the half life of the radioactive substance?

• A. $4$ days
• B. $6$ days
• C. $2$ days
• D. $3$ days

Answer 1

Answer: (A)

$4$ days

The value of initial sample is $8000$. It decays in $4$ days to half of the initial value i.e. $4000$ atoms. In next four days, it further days to $2000$ atoms. In next four days, it will again decay to $1000$ atom i.e. half of the present initial value.
Hence,
$8000\underset{4}{\to }4000\underset{4}{\to }2000\underset{4}{\to }1000$
So, half life of sample $\left(T_{1/2}\right)=4days$.