Question

For a first order reaction , the time taken to reduce the initial concentrations by a factor of 1/4 is 20 minutes . The time required to reduce initial concentration by a factor of 1/16 is
A. 20 min
B. 10 min
C. 80 min
D. 40 min

Answer 1

Correct Answer - d
`1 overset(1^(st))to1//2 overset(2^(nd))to1//4overset(3^(rd))to1//8 overset(4^(th))to1//16`
1/16 is 4 half-lives and 1/4 is 2 half-lives . It is given that the time taken for 2 half-lives is 20 minutes . So the time taken for 4 half-lives will be 40 minutes .