The half-life of tritium or hydrogen-3 is it 12.32 years, after about 24.6 years how much of a sample of tritium remain unchanged?
a 1/3
b 1/2
c 1/8
d 1/4

The answer will be D, 1/4.

How you come to this conclusion( for future reference to anyone stuck on this ), is figure out how many half-lives have passed. In this case two half-lives have passed ( 24.6 is 12.32 + 12.32 ), so just put into your calculator 1/2 x 1/2 ( or .5 x .5 ). Make sure your answer is in fraction form, and you have your answer! Hope this helps any who may see this!