Question

A radioactive sample has initial activity of $28dpm$ $30$ minutes later its activity $14dpm$ How many atoms of nuclide were present initially?

• A. $2800$
• B. $1212$
• C. $528$
• D. $2802$

Answer 1

The correct option is B $1212$

Here, Half life $=30minutes$

$\therefore \lambda =\frac{l{n}^2}{30}=0.0231mi{n}^{-1}$

Activity $=\lambda N$

$\therefore$ Initial activity $=\lambda N_{\circ }$

$\therefore N_{\circ }=\frac{28}{\mathrm{0..231}}=1212$