A 208 grams sample of Sodium-24 decays. How much of this radioactive isotope will remain after 3 half lives?

To solve this problem, we need to understand how half-lives work. A half-life is the time it takes for half of a sample to decay.

1. Starting with 208 grams of Sodium-24, after the first half-life, half of it would remain:

– After 1 half-life: 208 grams / 2 = 104 grams

2. After the second half-life, again half of the remaining amount will decay:

– After 2 half-lives: 104 grams / 2 = 52 grams

3. After the third half-life, we repeat the process:

– After 3 half-lives: 52 grams / 2 = 26 grams

Thus, after 3 half-lives, 26 grams of Sodium-24 will remain.

The correct answer is a) 26 grams.