Question

The half life period of a radioactive mineral is $15min$. What percent of radioactivity of that mineral will remain after $45min$?

• A. $17.5$%
• B. $15$%
• C. $12.5$%
• D. $10$%

Answer 1

The correct option is C $12.5$%

$n=\frac{45}{15}=3=$ Number of half lives
$N=N_0{\left(\frac{1}{2}\right)}^n=100\times {\left(\frac{1}{2}\right)}^3=12.5$%