Question

Hydrazine (N2H4) is a chemical compound used in rocket fuel. Which of the following represents the correct balanced equation for the reaction of hydrazine liquid with oxygen gas to produce nitrogen gas and steam? A. N2H4 (l) + O (g) N (g) + H2O (g) B. N2H4 (l) + 2 O (g) 2 N (g) + 2 H2O (g) C. N2H4 (l) + O2 (g) N2 (g) + 2 H2O (g) D. N2H4 (l) + O2 (g) N2 (g) + H2O (g)

Answer 1

Answer is C.
N₂H₄(l) + O₂(g) → N₂(g) + 2H₂O(g)

liquids should be denoted as (l) and gasses should be (g) including steam.
the natural form of oxygen gas and nitrogen gas are O₂ and N₂ respectively. 
Left hand side of equation:
N atoms = 2
H atoms = 4
O atoms = 2

Right hand side of equation:
N atoms = 2
H atoms = 2
O atoms = 1

hence the quation is imbalanced.
So 2 should be added at the left hand side of H₂O