75% of a first order reaction is completed in 32 min. 50% of the reaction would have been completed in

Options

A. 24min
B. 16min
C. 18min
D. 24min

Answer

B

Explanation

For first order reaction,
`k=(2.303/t)"log"(a/(a-x))`
`k=(2.303/t)"log"(a/(a-0.5a)) ( because x= (75/100) a=0.75a)`
`k=0.0433 mi n^(-1)`
For 50% of reaction, time (t)`=(2.303/t)"log"(a/(a-0.5a))`
`=(2.303/0.0433)"log"(1/1.5)`
` therefore t=16`.