Answer:
Step-by-step explanation:
I think you mean
2N2H4 + N2O4 ==> 3 N2 + 4H2O
The equation says that for Every mol of N2O4, you need 2 moles of N2H4.
1/2 = x/3,5 Multiply both sides by 3.5
3.5*1 / 2 = x
1.75 = x
Therefore you need 1.75 moles N2O4 are needed for 3.5 moles of N2H4