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 $${}^1H$$ atoms are replaced by $${}^2H$$ atoms is
A.
15 $$kg$$
B.
37.5 $$kg$$
C.
7.5 $$kg$$
D.
10 $$kg$$
Answer :
7.5 $$kg$$
Solution :
Percentage (by mass) of elements given in the body of a healthy human adult is :-
$$\eqalign{
& {\text{Oxygen}} = 61.4\% ,\,{\text{Carbon}} = 22.9\% , \cr
& {\text{Hydrogen}} = 10.0\% \,{\text{and}}\,{\text{Nitrogen}} = 2.6\% \cr
& \because {\text{Weight}}\,{\text{of}}\,{\text{person}} = 75\,kg \cr
& \therefore \,\,{\text{Mass}}\,{\text{due}}\,{\text{to}}\,{}^1H\,{\text{is}} = 75 \times \frac{{10}}{{100}} = 7.5kg \cr
& {\text{If}}\,{}^1H\,{\text{atoms}}\,{\text{are}}\,{\text{replaced}}\,{\text{by}}\,{}^2H\,{\text{atoms,}} \cr
& {\text{mass}}\,{\text{gain}}\,{\text{by}}\,{\text{person}}\,{\text{would}}\,{\text{be}} = 7.5\,kg \cr} $$