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 kg person would gain if all $${}^{\text{1}}\text{H}$$ are replaced by $${}^{\text{2}}\text{H}$$atoms is
a.) 15 kg
b.) 37.5 kg
c.) 7.5 kg
d.) 10 kg

Answer 1

Hint: Solve this question by calculating the mass of hydrogen using the given percentage. Also note that $${}^{\text{1}}\text{H}$$ and $${}^{\text{2}}\text{H}$$ are isotopes of hydrogen.

Complete step by step answer:
According to the question,
Weight of the person = 75 kg
Mass % of Oxygen = 61.4 %
Mass % of Carbon = 22.9 %
Mass % of Hydrogen = 10 %
Mass % of Nitrogen = 2.6 %
Therefore, mass of $${}^{\text{1}}\text{H}$$= 10 % of 75 kg = 7.5 kg
Since $${}^{\text{2}}\text{H}$$ is double the mass of $${}^{\text{1}}\text{H}$$,
Therefore, mass of $${}^{\text{2}}\text{H}$$= 2 x 7.5 kg = 15 kg
According to the question, all$${}^{\text{1}}\text{H}$$ are replaced by $${}^{\text{2}}\text{H}$$.
So, the increase in weight = weight of $${}^{\text{1}}\text{H}$$ – weight of $${}^{\text{2}}\text{H}$$= 15 – 7.5 kg = 7.5 kg
Therefore, the answer is – option (c) – If all $${}^{\text{1}}\text{H}$$ are replaced by $${}^{\text{2}}\text{H}$$, the weight gained by the person is 7.5 kg.

Note: “Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom”.
There are three isotopes of hydrogen, namely - protium ($${}^{\text{1}}\text{H}$$), deuterium ($${}^{\text{2}}\text{H}$$) and tritium ($${}^{\text{3}}\text{H}$$).