Question

The time taken for 10% completion of a first order reactin is 20 mins. Then, for 19%  completion, the reaction will take 

• (A) 40 min
• (B) 60 min
• (C) 30 min
• (D) 50 min

Answer 1

The Correct Option is A

Explanation:
$$\begin{array}{c}t=\frac{2.303}{\lambda }\log \frac{N_0}{N}\\ 20=\frac{2.303}{\lambda }\log \frac{100}{90}\\ t=\frac{2.303}{\lambda }\log \frac{100}{81}\end{array}$$equation (i) / (ii) $\therefore t=40min$