If half-life of a substance is $$5$$ $$yrs,$$ then the total amount of substance left after 15 years, when initial amount is $$64$$ $$grams$$ is
A.
16$$\,g$$
B.
2$$\,g$$
C.
32$$\,g$$
D.
8$$\,g$$
Answer :
8$$\,g$$
Solution :
$${t_{\frac{1}{2}}} = 5\,{\text{years,}}\,T = 15\,{\text{years}}$$ hence total number of half life periods $${\text{ = }}\frac{{15}}{5} = 3$$
∴ Amount left $$ = \frac{{64}}{{{{\left( 2 \right)}^3}}} = 8g$$
Releted MCQ Question on Physical Chemistry >> Chemical Kinetics
Releted Question 1
If uranium (mass number 238 and atomic number 92) emits an $$\alpha $$ -particle, the product has mass no. and atomic no.