Half-life of radioactive sample, when activity of material initially was 8 counts and after 3 hours it becomes 1 count is

Options

A. 2 hours
B. 1 hour
C. 3 hours
D. 4 hours

Answer

B

Explanation

`R_(0) = 8, R=1, t= 3hr`
`(R)/(R_(0)) = ((1)/(2))^(n) rArr (1)/(8) = ((1)/(2))^(n) rArr n= 3`
Now, `(t)/(T_(1//2)) = 3 rArr T_(1//2) = (3)/(3) =1` hr