Question

after two half-lives how much of the parent element is left?
12.5%
25%
100%
50%

Explanation:

Step1: Understand Half - Life Concept

A half - life is the time it takes for half of a radioactive (parent) element to decay. Let's assume the initial amount of the parent element is \(A_0 = 100\%\) (we can use 100% for simplicity, but it could be any initial amount).

Step2: After First Half - Life

After one half - life, the amount of the parent element remaining is half of the initial amount. So, if \(A_0\) is the initial amount, after one half - life \(A_1=\frac{A_0}{2}\). If \(A_0 = 100\%\), then \(A_1=\frac{100\%}{2}=50\%\).

Step3: After Second Half - Life

After the second half - life, the amount remaining is half of the amount that was present after the first half - life. So, \(A_2=\frac{A_1}{2}\). Since \(A_1 = 50\%\), then \(A_2=\frac{50\%}{2}=25\%\).

Answer:

25% (The option with 25%)