There are two gas parcels of equal volume, A and B at the same temperature and pressure. Parcel A is one mole of water vapour, while parcel B is one mole of day air. Which of the following is TRUE?

Correct option is B

Given:

• Two gas parcels (A and B)

• Same volume, temperature, and pressure

• Parcel A:1 mole of water vapour (H₂O)

• Parcel B:1 mole of dry air

Concept Used:
At the same temperature and pressure, the mass of one mole of a gas is simply its molar mass.

• Molar mass of water vapour (H₂O) = 18 g/mol

• Molar mass of dry air (approximate) = 78% N₂ (28 g/mol) + 21% O₂ (32 g/mol)
  → Weighted average ≈ 29 g/mol

Solution:

• Parcel A (water vapour): 18 g

• Parcel B (dry air): 29 g

So, Parcel B is heavier than Parcel A

Correct Option: (B) Parcel B is heavier than Parcel A