Answer:
3.50 M
Explanation:
Step 1: Write the balanced equation
4 NH₃(g) + 7 O₂(g) ⇄ 2 N₂O₄(g) + 6 H₂O(g)
Step 2: Make an ICE chart
    4 NH₃(g) + 7 O₂(g) ⇄ 2 N₂O₄(g) + 6 H₂O(g)
I Â Â Â Â Â Â Â 0 Â Â Â Â Â Â Â 0 Â Â Â Â Â Â Â 3.60 Â Â Â Â Â Â 3.60
C     +4x       +7x        -2x       -6x
E       4x        7x      3.60-2x    3.60-6x
Step 3: Calculate the value of x
The concentration of water at equilibrium is 0.600 M. Then,
3.60-6x = 0.600 M
x = 0.500 M
Step 4: Calculate the concentration of Oâ‚‚ at equilibrium
The concentration of Oâ‚‚ at equilibrium is 7x = 7(0.500M) = 3.50 M