A radioactive material of half- life T was produced in nuclear reactor at different instants , the quantity produced second time was twice of that produced first time.If now their present activities are A1 and A2 respectively then their age difference equals: (a) T/ln2×|lnA1/A2| (b) T×|lnA1/A2| (c) T/ln2×| lnA2/2A1| (d) T|lnA2/2A1| ans:- (c)