1.386 hours are required for the disappearance of 75% of a reactant of first-order reaction. What is the rate constant of the reaction?

Let original amount N0=100Since, disappeared amount = 75%∴ left amount, N=100−75=25∴ Since, N0N=2n where n = no. of half lives  10025=2n 22=2n, here n=2∵ Total time =n×t1/21.386 hours =2×t1/2, t1/2=0.693 hours      =2494.8 sec.   k=0.6932494.8=2.7×10−4 sec-1