What is name of the lightest gas in the universe?

a) Oxygen

b) Nitrogen

c) Helium

d) Hydrogen 

Hydrogen is not only the lightest gas, but it is also most abundant gas in the universe. A total of 90% of all the atoms is of Hydrogen. Hydrogen (H2) has an atomic number of 1 and atomic mass 1.00794 amu. Note that the heaviest gas in the world is Tungsten Hexafluoride (WF6) .