The correct option is B 150 min
For first order reaction,
t=2.303klog10R0R→initial concentration→left out concentration
75% reaction completed in 100 min than rate constant is ∴R0=100;R=100−75=25
k=2.303tlog1010025
k=2.303100log1010025
k=2.303100log104
Time taken for completion of 87.5% of the reaction; (∴R0=100;R=100−87.5=12.5)
t=2.303klog1010012.5
On substituting the value of k in equation we get,
t=2.303log1082.303100log104=100×log108log104
=100×1.5
=150 min