Question

The most abundant elements by mass in the body of a healthy human adult are : Oxygen $\left(61.4\%\right)$; Carbon $\left(22.9\%\right)$, Hydrogen $\left(10.0\%\right)$; and Nitrogen $\left(2.6\%\right)$. The weight which a 75 kg person would gain if all ${}^{1}H$ atoms are replaced by ${}^{2}H$ atoms is :

• A. $37.5kg$
• B. $7.5kg$
• C. $10kg$
• D. $15kg$

Answer 1

Answer: (B)

$7.5kg$

Hydrogen is $10.0\%$.
Body weight $=$ $75$ kg
Mass of H-1 $=75\times \frac{10.0}{100}=7.5kg$
When H-1 is replaced with H-2 the weight gain will be equal to original mass of H-1 which is $7.5$ kg.
Hence, the option (B) is the correct answer.