What percentage of daughter atoms remain after 2 half-lives have elapsed? ?
25%
75%
100%
50%
The correct answer and explanation is:
The correct answer is 25%.
To explain this, half-life refers to the time it takes for half of the original amount of a radioactive substance to decay into its daughter atoms. After one half-life, 50% of the original substance will have decayed, and 50% will remain as parent atoms.
After two half-lives, the amount of parent atoms will have reduced by half again, meaning only 25% of the original parent atoms remain. In contrast, 75% of the original parent atoms will have decayed into daughter atoms. Thus, after two half-lives, 25% of the original parent atoms remain, and 75% have decayed.
To visualize this:
- After 1 half-life, 50% of the original substance decays into daughter atoms.
- After 2 half-lives, another 50% of the remaining parent atoms decay, leaving 25% of the original parent atoms.
This process continues with each half-life halving the amount of the original substance, and therefore, increasing the amount of daughter atoms. So, after 2 half-lives, 25% of the original parent atoms remain and 75% have decayed into daughter atoms.