a sample is in the second half - life. what percent of the sample is stable at this point?\n12.5%\n25%\n50%\n…

Explanation:

Step1: Understand half - life concept

The amount of a radioactive substance remaining after each half - life follows an exponential decay pattern. After the first half - life, 50% of the original sample remains radioactive and 50% has decayed (become stable).

Step2: Analyze the second half - life

After the second half - life, half of the remaining radioactive substance decays. So if 50% was radioactive after the first half - life, then after the second half - life, half of that 50% decays. The amount of the sample that is still radioactive after the second half - life is $0.5\times0.5 = 0.25$ or 25%. The amount that is stable is $1 - 0.25=0.75$ or 75%.

Answer:

75%