Which compound in each pair of isomers is the stronger acid?

a.

or

b.

or

A compound that easily produces ${\mathbf{H}}^{\mathbf{+}}$ ions by the dissociation of a bond is said to be acidic.

The hydrogen atoms attached/bonded to electronegative atoms are more acidic. They pull the electron density of the bond towards themselves, leading to the dissociation of the bond.

a.

Pair of isomers given in a

In case a, molecule 1 consists of two hydrogen atoms directly bonded to the nitrogen atom. Molecule 2 consists of hydrogen atoms bonded to carbon atoms.

Therefore, molecule1 is more acidic as nitrogen is more electronegative than carbon.

b.

Pair of isomers given in b

In the case of b, molecule 2 consists of a hydrogen atom directly bonded to the oxygen atom. In molecule 1, all hydrogen atoms are bonded to carbon atoms.

Since oxygen is more electronegative than carbon, the hydrogen attached to it can easily dissociate into ${\mathrm{H}}^{+}$.

Therefore, molecule 2 is more acidic.