Question

You find a rock sample with radioactive atoms present. 25% of the original radioactive atoms were present, how many half lives have passed

Answer 1

Im literally taking a test that my teacher made and i have no idea what the answer is

Step-by-step explanation:

Answer 2

The two half-lives are needed to reach 25% remaining. Therefore, the answer is 2.

We determine how many half-lives have passed in the rock sample, we can use the following logic:

In each half-life, the number of radioactive atoms remaining is halved.

If 25% of the original atoms remain, this means 75% have decayed.

Therefore, we need to find the number of half-lives it takes for 75% of the atoms to decay:

First half-life: 50% remaining (original 100% - 50% decay = 50%)

Second half-life: 25% remaining (50% - another 50% decay = 25%)