The rate constant at `25^(@)C` for the reaction of `NH_(4)^(+)` and `OH^(-)` to form `NH_(4)OH` is `4xx10^(10) M^(-1) sec^(-1)` and ionisation constant of aq. `NH_(3)` is `1.8xx10^(-5)`. The rate constant of proton transfer to `NH_(3)` is

Options

A. `1.8xx10^(-5)`
B. `7.2xx10^(5)`
C. `3.6xx10^(5)`
D. `4.2xx10^(-5)`

Answer

B

Explanation

`NH_(4)^(+)+OH^(-)overset(k_(1))(to) NH_(4)OH` , `k_(1)=4xx10^(10)`
`NH_(4)OHoverset(K_(f))underset(K_(b))(hArr)NH_(4)^(+)+OH^(-)`
`k_(eq)=(k_(f))/(k_(b))`
`1.8xx10^(-5)=(k_(f))/(4xx10^(10)) implies k_(f)=7.2xx10^(5)`