In a first order reaction, `75%` of the reactants disappeared in `1.386 hr`. What is the rate constant ?

Options

A. `3.6xx10^(-3) s^(-1)`
B. `2.8xx10^(-4) s^(-1)`
C. `17.2xx10^(-3) s^(-1)`
D. `1.8xx10^(-3) s^(-1)`

Answer

B

Explanation

75% disappears in 1.388 hr. so 50% disappears in `(1.388)/(2) hr`
or `0.694" hr. k"=(0.693)/(t_(1//2))=(0.693)/(0.694xx60xx60)"sec"^(-1)~~(100)/(36)xx10^(-4)s^(-1)=2.8xx10^(-4) s^(-1)`