I figured out that 4 moles of ammonia is needed to react with 5 moles of oxygen to give 4 moles of NO.
OK, that's one of the ways of reading what the balanced reaction equation says.
now it is 0.1 mole, which is 2% of 5moles,
Beware: when you say "it is 0.1 mole" we have no idea 0.1 mole of what, as there are two substances with the same amount given in the problem. Later you refer to 5 moles, so we can guess you meant O2
, but you should never assume people will guess right.
so it should take 0.08 mole of ammonia and the amount of NO produced should be 0.08 mole.
Assuming you meant "0.1 mole of oxygen" above - yes.
but there is no "0.08 mole" in the answer of this MC question.
Which looks like an error in the test.
In addition which one is limiting reagent? Ammonia or oxygen?
The best approach to finding the limiting reagent is to do the calculations several times, separately for each of the reagents with given initial amount.
How many moles of ammonia would react with 0.1 moles of oxygen? Is there enough ammonia?
How many moles of oxygen would react with 0.1 moles of ammonia? Is there enough oxygen?