Question

The half life of a radioactive substance is `20` minutes . The approximate time interval `(t_(2) - t_(1))` between the time `t_(2)` when `(2)/(3)` of it had decayed and time `t_(1)` when `(1)/(3)` of it had decay is
A. `14 min`
B. `20 min`
C. `28 min`
D. `7 min`

Answer 1

Correct Answer - B
At `t_(1) (2)/(3)=(1)/(2^(t_(1)//20))` At `t_(2)=(1)/(3)=(1)/(2^(t_(2)//20))`
`t_(2)-t_(1)=20 "mins"`