Question

A radioactive substance contains $10,000$ nuclei and its half life period is $20$ days. The number of nuclei present at the end of $10$ days is

• A. 7500
• B. 8000
• C. 9000
• D. 7070

Answer 1

Answer: (D)

7070

Answer 2

We know, $\frac{N}{N_{0}}=\left(\frac{1}{2}\right)^{1 / T}$
$\Rightarrow \frac{N}{10000}=\left(\frac{1}{2}\right)^{1020}$
$\Rightarrow N=\frac{10000}{\sqrt{2}}$
$=\frac{10000}{1.414}$
$=7070$