You use 86.3 g #NO #and 25.6 g #H_2# in an experiment and produce 49.0 g of ammonia. How much excess reactant was used to make the 49.0 g of ammonia?
We need (i) a stoichiometric equation.....
Which (I think) is balanced, as indeed it must be if we purport to represent chemical reality.
And then (ii) we work out equivalent quantities of product and reactant.
So you have got
The excess dihydrogen is simply