Question

Radioactive decay follows first - order kinetics. The initial amount of two radioactive elements X and Y is 1 gm each. What will be the ratio of X and Y after two days if their halflives are 12 hours and 16 hours respectively?

Answer 1

For first order reaction 

half life of X = 12 hours 

2 days = 48 hours means 4 half lives , amount of X left = 1/16 of initial value

half life of Y = 16 hours 1/2 2 days = 48 hours means 3 half lives, amount left = 1/8 of initial value 

Ratio of X:Y = 1:2