Thorium-234 has a half-life of 24.1 days. how much of a 100-g sample of thorium-234 will be unchanged after 48.2 days?

Half-life means that the matter degrades by 50% at each interval. 48.2 days is 2 intervals.

So, it would go down by 50% in the first interval, making it 50g. Then it would go down by another 50% from there, making the final amount of undecayed thorium-234 25g.

The answer options is d

It’s the energy source of stars