# The atomic composition of the entire universe is approximately given in the table below

 Atom % of total no of atoms H 93 He 7

Hydrogen atoms constitute what percentage of the universe by mass ?

$(a)\;77\%\qquad(b)\;23\%\qquad(c)\;37\%\qquad(d)\;73\%$

mass of 93 'H' atoms =93amu
mass of 7 'He' atoms =28amu
$\therefore$ % of hydrogen by mass =$\large\frac{93}{(93+28)}$$\times 100$
$\Rightarrow 77\%$
Hence (a) is the correct answer.