Question

The half-life of a radioactive substance is $10$ days. This means that

• A. the substance completely disintegrates in 20 days
• B. the substance completely disintegrates in 40 days
• C. 1/8 part of the mass of the substance will be left intact at the end of 40 days
• D. 7/8 part of the mass of the substance disintegrates in 30 days

Answer 1

Answer: (D)

7/8 part of the mass of the substance disintegrates in 30 days

Answer 2

In $30$ days (ie $3$ half-lives) So. $\left(\frac{1}{2^{3}}\right)=\frac{1}{8}$ of the substance is left or $\frac{7}{8}$ part of the mess of the substance disintegrate