In chemical reactions the reactants are on the left side of the equation and the product are on the right
I believe that the chemical formula for an acid often begins with H, which means C is your answer.
Answer:
23
Explanation:
if if you look at the screenshot it has the explanation
Answer: (D) 0.025 mol 
Explanation:
The given balanced equation is :

According to stoichiometry :
4 moles of ammonia
reacts with = 5 moles of oxygen 
Thus 0.30 moles of ammonia
reacts with =
moles of oxygen 
Now as given moles of oxygen are more than the required amount, oxygen is the excess reagent.
moles of oxygen
left = 0.40 - 0.375 = 0.025
Thus 0.025 mol
excess reagent remains.