Question

Among the following oxides, the correct order of acidity is:

• A. > > >
• B. > > >
• C. < < <
• D. > > >

Answer 1

The correct option is A > > >

First, let us get $N_{2}O$ out of our ways. It is a neutral oxide and should easily be the least acidic of the options given. Although NO is not given, do recall that NO is also a neutral oxide.
A good approach to solving this problem is to predict which oxide gives the most acidic acid on hydrolysis. What will be the correlation between the acidity of the acid and the oxidation state of the central Nitrogen atom?
Suppose, Nitrogen is in its highest (positive) oxidation state. That would mean that such a Nitrogen atom will have the greatest need for electrons. When the central atom is much more desperate for electrons, it will try to pull electrons from Oxygen. Oxygen, being more electronegative than Nitrogen, will tend to hold onto its surrounding electrons more tightly and this means that the removal of $H^{+}$ from the H – O bond will be easier. In other words, greater is the oxidation state on the nitrogen, greater will be the acidity:
Decreasing order of acidity is: $N_2{O}_5$ > $N{O}_2$> $N_2{O}_3$ > $N_{2}O$ (Oxidation states of nitrogen include +5 in $N_2{O}_5$, +4 in $N{O}_2$, +3 in $N_2{O}_3$, +1 in $N_{2}O$ )