(i) H₂O

Atomic Mass of Hydrogen = 1g

Atomic Mass of Oxygen = 16g

From the molecular formula of water, it is understood that in 1 mole of water, 2 moles of hydrogen and 1 mole of oxygen is present.

So Molecular Mass of Water = [2×1] + [16×1]

= 2 + 16

= 18g

Therefore, the molecular mass of water is 18g

(ii) CO₂

Atomic Mass of Carbon = 12g

Atomic Mass of Oxygen = 16g

From the molecular formula of carbon dioxide, it is understood that in 1 mole of carbon dioxide, 1 mole of carbon and 2 moles of oxygen is present.

So Molecular Mass of Carbon Dioxide = [12×1] + [16×2]

= 12 + 32

= 44g

Therefore, the molecular mass of carbon dioxide is 44g

(iii) CH₄

Atomic Mass of Carbon = 12g

Atomic Mass of Hydrogen = 1g

From the molecular formula of methane, it is understood that in 1 mole of methane, 1 mole of carbon and 4 moles of hydrogen is present.

So Molecular Mass of Methane = [12×1] + [4×1]

= 12 + 4

= 16g

Therefore, the molecular mass of methane is 16g