Question

Half-life of $B{i}^{210}$ is $5$ days. If we start with $50,000$ atoms of this isotope, the number of atoms left after $10$ days is

• A. $5,000$
• B. $25,000$
• C. $12,500$
• D. $20,000$

Answer 1

The correct option is C $12,500$

We know that $N_t=N_0{\left(\frac{1}{2}\right)}^{t/T}$,
where $t$ is time and $T$ is half life.
Putting the values,
$N_t=50000{\left(\frac{1}{2}\right)}^{10/5}=12500$