(a) Given, Mass of oxygen gas = 12g

Molar mass of oxygen gas = 2 × Mass of Oxygen = 2 × 16 = 32g

\( Number \ of \ moles \ = \) \( Mass \ given \over molar \ mass \ of \ oxygen \ gas \) \( = \) \( 12 \over 32 \) \( = 0.375 \ moles \)

(b) Mass of water = 20g

Molar mass of water = 2 × Mass of Hydrogen + Mass of Oxygen = 2 × 1 + 16 = 18g

\( Number \ of \ moles \ = \) \( Mass \ given \over molar \ mass \ of \ water \) \( = \) \( 20 \over 18 \) \( = 1.11 \ moles \)

(c) Mass of carbon dioxide = 22g

Molar mass of carbon dioxide = Mass of C + 2 × Mass of Oxygen = 12 + 2 × 16 = 12 + 32 = 44g

\( Number \ of \ moles = \) \( Mass \ given \over molar \ mass of \ carbon \ dioxide \) \( = \) \( 22 \over 44 \) \( = 0.5 \ moles \)