The thermal decomposition of a compound is of first order. If `50%` of a sample of the compound is decomposed in 120 minutes, how long it take for `90%` of the compounds to decompose.

Explanation

Rate constant(k)`=(0.693)/(t_(1//2))=0.693/(120"min")`
`t=(2.303 xx 120"min")/(0.693) = 399 "minutes"`.