Question

What fraction of a radioactive material will get disintegrated in a period of two half-lives?

• A. Whole
• B. Half
• C. One-fourth
• D. Three-fourth

Answer 1

Answer: (D)

Amount of radioactive material left after two half-lives
$N=N_0{\left(\frac{1}{2}\right)}^{2T/T}=\frac{N_0}{4}$
$\therefore$ Radioactive material decayed
$=N_0-\frac{N_0}{4}=\frac{3}{4}{N}_0$
Thus, three-fourth part of the radioactive material will get disintegrated after two half-lives.