In a old rock, ratio of nuclei of uranium and lead is 1 : 1. Half life of uranium is `4.5 ×6 10^(9)` yrs. Let initially it contains only uranium nuclei. How old is the rock ?

Explanation

Let present active nuclei of uranium is N then intial
active nuclei is 2N.
Present active fraction of uranium
` = (1)/(2) " r " (1)/(2) = (1)/(2^(1//n_(1//2)))`
`" or " (t ) /(T_(1//2))= 1`
` " or " t= T_(1//2) = 4.5 xx 10^(9) Yr`