Question

The half-life of radium is 1600 years. The fraction of a sample of radium that would remain after 6400 years :

• A. 1/4
• B. 1/2
• C. 1/8
• D. 1/16

Answer 1

The correct option is D 1/16

As radioactive decay is first-order kinetic

half-life given is $1600$ years in $6400$ no. of half-life is

n$=\frac{6400}{1600}=4$

fraction of element remains after n half life is given by $=\frac{1}{2^n}$

Hence fraction of radium remains after $4$ half life

$=\frac{1}{2^4}=\frac{1}{16}$.

Option D.