Question

Half life of iodine -131is 8days and its weight is 20mg After 4half lives the amount left undecayed will be?

Answer 1

The initial amount is 20 miligrams right?

Explanation:

You have total 32 days (4 half life periods (number of arrows in the figure provided below).

The original amount 20 mg.

`20 mg -> 10 mg -> 5 mg -> 2.5 mg -> 1.25 mg`

The amount left after 32 days (4 half life periods) will be 1.25 miligrams.