Step I: Calculation of rate constant.
`a=100% (a-x) = 25%, t=60 min`.
for first order reaction,
`k=(2.303)/k log a/(a-x) = (2.303)/(60"min") log 100/25`
`=(2.303)/(60 "min") xx log4 = (2.303 xx 0.6020)/(60 min) = 0.0231 min^(-1)`
Step II: Calculation or half life period `(t_(1//2))`
`t_(1//2) = 0.693/k = (0.693)/(0.0231 min^(-1))=30 min`
