The reaction, A→B follows first order kinetics. Initial concentration of ‘A’ is 4 M. Rate of the reaction after 100 minutes will be (Half life period of the reaction =100 minutes)

For a first order reaction; K=0.693t12=0.693100min-1; Amount left,(a-x)=Initial amounta2n; n=number of half lives; n=100100=1; (a-x)=421=2 M; After 100 minutes, rate=K(a-x)1; rate=0.693100(2) rate=1.386×10-2mol lit-1min-1