Question

The half-life of a radio-isotope is $4hr$. If initial mass of the isotope was $200g$, then mass remaining after $24hr$ will be

• A. $1.042g$
• B. $2.084g$
• C. $3.125g$
• D. $4.167g$

Answer 1

Answer: (C)

$3.125g$

Remaining mass after $n$ half lives is $\frac{1}{2^n}$ the initial mass.

In this case the number of half lives passed is $\frac{24}{4}=6$

So the remaining mass $=\frac{200}{64}=3.125g$