Question

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

• A. $15\text{kg}$
• B. $37.5\text{kg}$
• C. $7.5\text{kg}$
• D. $10\text{kg}$

Answer 1

The correct option is C $7.5\text{kg}$

H is 10% by mass
$\therefore$ $H$ is $7.5\text{kg}$.
It is replaced by ${}^{2}H$, so weight is doubled i.e., $15\text{kg}$
$\therefore$ $7.5\text{kg}$ increase in weight will be observed