The half-life of radioactive material is `3 h`. If the initial amount is `300 g`, then after `18 h`, it will remain:
(1.) 4.68g
(2.) 46.8g
(3.) 9.375g
(4.) 93.75g

Options

A. 4.68 g
B. 2.34 g
C. 1.17 g
D. 9.36 g

Answer

A

Explanation

Given
Half life `(t_(1//2))=3h`
Initial mass`(N_(0))=300 g`
Total time (T)=18 h
Mass left (N)=?
We know that ,
`(N)/(N_(0))=(1/2)^(n)`
where n =number of half lives
`n=("Total time")/("Half life")=(18)/(3)=6`
So `(N)/(300)=(1/2)^(6)`
or `(N)/(300)=(1)/(64)`
`N=(300)/(64)=4.68 g`