1.

The compounds are:

• I = Cyclohexane carboxylic acid
• II = Tetrahydropyran-2-carboxylic acid (O atom α to the carbon bearing –COOH)
• III = Tetrahydropyran-3-carboxylic acid (O atom β to the carbon bearing –COOH)

Key Concept

The –I (negative inductive) effect of oxygen increases the acidity of a carboxylic acid by stabilizing the carboxylate ion.

• The closer the oxygen atom is to the –COOH group, the stronger its –I effect.
• The inductive effect decreases rapidly with distance.

Comparison

• II: Oxygen is α to the carbon attached to –COOH → strongest –I effect → most acidic.
• III: Oxygen is β to the carbon attached to –COOH → weaker –I effect than II → intermediate acidity.
• I: No oxygen in the ring → no additional –I effect → least acidic.

Acidic strength order

$$\boxed{\text{II} > \text{III} > \text{I}}$$