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 (\[^{\text{3}}\text{H}\]).