The decay of the isotope iodine-131 is first-order with a rate constant of 0.138 d−1. all radioactive decay is first order. how many days will it take for 90% of the isotope to decay to xe-131?

16.7 days

Explanation:

We are given;

A radioactive isotope Iodine-131`

The decay rate is 0.138 d⁻¹

The percent decayed is 90%

We are suppose to calculate the number of days for the decay.

Where, is the initial concentration and is the new concentration.

Assuming the initial concentration is x, then the final concentration after 90% decay will be 0.10x

Therefore;

Time = 16.7 days

Therefore, it will take 16.7 days for 90% of I-131 to decay to Xe-131

the answer would be c