Answer :
Half life of the reaction is :-101.9 min
a→b
25% reacted means 75% remains
t=42 min
Rate constant
k=(2.303/t)(log a/a-x)
k=(2.303/42)(log 100/100-25 )
k=(0.054) (log 100/75)
k=(0.054)(0.1249)
k=0.0068per min
half life
t1/2=(0.693/k)
=(0.693/0.0068)
=101.9 min
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