Answer: 3.5 mol of oxygen
Explanation:
The unbalanced equation for this reaction is
[tex]\text{NH}_{3}+\text{O}_{2} \longrightarrow \text{N}_{2}+\text{H}_{2}\text{O}[/tex]
Balancing this equation,
[tex]4\text{NH}_{3}+3\text{O}_{2} \longrightarrow 2\text{N}_{2}+6\text{H}_{2}\text{O}[/tex]
From this, we can tell that for every 4 moles of ammonia consumed, 3 moles of oxygen are consumed.
This means that ammonia is the limiting reactant, meaning that 2.0(3/4)=1.5 moles of oxygen are consumed.
So, 5.0-1.5=3.5 mol of oxygen remain.