Question

after two half - lives, how much of the original material has decayed? 25 percent 50 percent 75 percent 100 percent

Explanation:

Step1: Define half - life concept

The amount of material remaining after one half - life is $50\%$ (or $\frac{1}{2}$) of the original amount.

Step2: Calculate after two half - lives

After the first half - life, the remaining amount is $\frac{1}{2}$ of the original. After the second half - life, the remaining amount is $\frac{1}{2}\times\frac{1}{2}=\frac{1}{4}$ of the original.

Step3: Calculate decayed amount

The decayed amount is $1-\frac{1}{4}=\frac{3}{4}$, which is $75\%$.

Answer:

C. 75 percent