Explain why the number of atoms in one mole of hydrogen gas is double the number of atoms in one mole of helium gas?

[LokeshCBSE]

1. Explain why the number of atoms in one mole of hydrogen gas is double the number of atoms in one mole of helium gas?
2. Explain atomic mass unit.
3. How many atoms are present in
   • MnO₂ molecule
   • CO molecule?

[LokeshCBSE]

1. Hydrogen gas exists as diatomic molecules, i.e. each hydrogen gas molecule (H₂) has two atoms. While helium gas exists as monoatomic particle that is its atoms exist individually. Thus, one mole of hydrogen gas has double number of atoms as compare to one mole of helium gas.
2. The unit of mass equivalent to the twelfth part of the mass of C-12 isotope of carbon is called atomic mass unit (amu) or unified mass (u).
3. • In MnO₂ molecule, three atoms are present: One manganese atom and two oxygen atoms.
   • In CO molecule, two atoms are present: One carbon atom and one oxygen atom.