Question

43. We have a radioactive isotope called RI which has a half-life of 12 million years. A geologist

Answer 1

Answer: Thus 3 half lives have taken place.

Explanation:

Expression for rate law for first order kinetics is given by:

$t=\frac{2.303}{k}\log\frac{a}{a-x}$

where,

k = rate constant

t = age of sample

a = let initial amount of the reactant

a - x = amount left after decay process  

a) for completion of half life:

Half life is the amount of time taken by a radioactive material to decay to half of its original value.

$t_{\frac{1}{2}}=\frac{2.303}{k}\log\frac{100}{50}$

$t_{\frac{1}{2}}=\frac{0.693}{k}$

Number of half lives =$\frac{\text {total time}}{\text {half life}}=\frac{36million}{12million}=3$

Thus 3 half lives have taken place.