1)

A first-order reaction is 25 % completed in 40 minutes. What is the rate constant k for the reaction?

A) $\frac{2.303\times \log1.33}{40}$

B) $2.303\times \log\frac{4}{3}$

C) $\frac{2.303\times \log4}{40\times3}$

D) $\frac{2.303 }{40}\times\log \frac{1}{4}$

Option A

### Explanation:

Given,

Time (t)= 40 min

a=100

(a-x)=100-25=75

First order  reaction,

$Rate(k)=\frac{2.303}{t}\log\left(\frac{a}{a-x}\right)=\frac{2.303\times\log 1.33}{40}$