1g H₂ contains a maximum number of molecules.

The molecules present in the 1g CO₂:

Molar mass of CO₂ = 44g

The number of molecules

=

= 0.02N_A

The molecules present in the 1g N₂ :

Molar mass of N₂ = 28g

The number of molecules

=

= 0.03N_A

The molecules present in the 1g H₂ :

Molar mass of N₂ = 2g

=

= 0.5N_A

The molecules present in the 1g CH₄ :

Molar mass of CH₄ = 16g

=

= 0.06N_A

Thus, we can see that 1g H₂ contains the highest number of molecules.