4) 4 nh3 + 3 o2  2 n2 + 6 h2o

a. write the mole ratio for nh3 to n2

b. write the mole ratio for h2o to o2

4 NH₃ + 3O₂ --> 2N₂ + 6H₂O

First, make sure that this is a balanced equation.
There are 4 moles of nitrogen on the left side, and 4 moles of nitrogen on the right side.
There are 12 moles of hydrogen on the left side, and 12 moles of hydrogen on the right side.
There are 6 moles of oxygen on the left side, and 6 moles of oxygen on the right side.

The equation is therefore balanced, and we may proceed.

a) the mole ratio for NH₃ to N₂ is 4 to 2, which can be simplified to 2:1 or 2/1.

b) the mole ratio for H₂O to O₂ is 6 to 3, which can be simplified to 2:1 or 2/1.