Question

18 multiple choice 1 point after 2 half lives how much of the original material is still there? 25% 100% 12.5% 50%

Explanation:

Step1: Recall half - life concept

The half - life of a substance is the time it takes for half of the substance to decay. After one half - life, the amount of the original substance remaining is $50\%$ (or $\frac{1}{2}$) of the original amount.

Step2: Calculate after two half - lives

After the first half - life, the remaining amount $N_1=\frac{1}{2}N_0$ (where $N_0$ is the original amount). After the second half - life, the amount remaining $N_2=\frac{1}{2}N_1$. Substituting $N_1 = \frac{1}{2}N_0$ into the equation for $N_2$, we get $N_2=\frac{1}{2}\times\frac{1}{2}N_0=\frac{1}{4}N_0$. To convert $\frac{1}{4}$ to a percentage, we multiply by 100, so $\frac{1}{4}\times100 = 25\%$.

Answer:

25% (the option corresponding to 25%)