Tritium has a half-life of 12.3 years. When the activity of a tritium sample has decreased to 6.25% of its original value, how many years have passed

t = 49.20 years

Explanation:

Half life expression for first order kinetic is:

Half life = 12.3 years

Where, k is rate constant

So,  

The rate constant, k = 0.05635 years⁻¹

Using integrated rate law for first order kinetics as:

Where,  

is the concentration at time t

is the initial concentration

Given:

is 6.25 % of . So,

= 0.0625

t = ?

t = 49.20 years