In a first order reaction, the concentration of the reactant decreases form `0.8 M` to `0.4 M` in `15 min`. The time taken for the concentration to change form `0.1 M` to `0.025 M` is

Options

A. 30 minutes
B. 60 minutes
C. 7.5 minutes
D. 15 minutes

Answer

A

Explanation

`t_(1//2)=15` minutes
For a first order reaction,
`[A]_(t)=([A]_(0))/(2^(n))`
`2^(n)=([A]_(0))/([A]_(t))=(200)/(50)`
`2^(n)=rArrn=2`
No. of half lines = 2
`:.` Time taken `= 2 xx t_(1//2)`
`= 2 xx 15 min = 30 min`.