Answer is 166.16 mins.
Explanation:
we have the relation between the half life and the rate constant as half life
t1/2=.693/k
k is the rate constant
or k=.693/t1/2 =.693/25 min-1
=2.772*10-2 min-1
time required for 25% completion
k=2.303/t x log (initial conc/final conc)
2.772*10-2=2.303/t x log (100/1)
t=166.16 min