Thallium-201 is a radioactive isotope that undergoes first-order decay. when the concentration of 201tl is 0.0042 m, its half-life is 73.0 hours. what is the half-life of 201tl when its concentration is 0.0136 m? (a) 51.0 hours(b) 73.0 hours(c) 123 hours(d) 236 hours

(B) 73.0 hours.

Explanation:

It is known that the decay of a radioactive isotope isotope obeys first order kinetics.Half-life time is the time needed for the reactants to be in its half concentration.If reactant has initial concentration [A₀], after half-life time its concentration will be ([A₀]/2).Also, it is clear that in first order decay the half-life time is independent of the initial concentration.

So, the half-life of 201Tl when its concentration is 0.0136 M is (B) 73.0 hours.