Answer: the reactant left in excess is H₂, and the amount of excess H₂ is 4.5 moles - 3 moles = 1.5 moles.
Explanation: Moles of N₂ = mass of N₂ / molar mass of N₂
Moles of N₂ = 56 g / 28 g/mol = 2 moles
Moles of H₂ = mass of H₂ / molar mass of H₂
Moles of H₂ = 9 g / 2 g/mol = 4.5 moles