Question

Explain Why?

"The number of atoms in a certain volume of hydrogen is twice the number of atoms in the same volume of helium at the same temperature and pressure."

Answer 1

This is due to Avogadros Law which states Equal volumes of all gases under similar conditions of temperature and pressure contain the same number of molecules.

Now volume of hydrogen gas = volume of helium gas

n molecules of hydrogen = n molecules of helium gas

nH₂ = nHe

1 mol. of hydrogen has 2 atoms of hydrogen and I molecule of helium has 1 atom of helium

Therefore 2H = He

∴ atoms in hydrogen is double the atoms of helium.