The final product 'A' in the following reaction sequence

We need to find the final product A in the reaction sequence where butanone reacts with HCN, followed by treatment with 95% $$H_2SO_4$$ and heat.

Butanone ($$CH_3CH_2COCH_3$$) undergoes nucleophilic addition with HCN to form a cyanohydrin:

$$CH_3CH_2COCH_3 + HCN \rightarrow CH_3CH_2C(OH)(CN)CH_3$$

The product is 2-hydroxy-2-methylbutanenitrile.

Concentrated $$H_2SO_4$$ (95%) acts as both a dehydrating agent and a hydrolysis catalyst:

First, the nitrile group ($$-CN$$) is hydrolyzed to a carboxylic acid group ($$-COOH$$) in the acidic medium:

$$CH_3CH_2C(OH)(CN)CH_3 \xrightarrow{H_2SO_4} CH_3CH_2C(OH)(COOH)CH_3$$

Then, dehydration occurs — the hydroxyl group and a hydrogen from the adjacent carbon are eliminated:

$$CH_3CH_2C(OH)(COOH)CH_3 \xrightarrow{-H_2O} CH_3CH=C(CH_3)COOH$$

The final product is $$CH_3-CH=C(CH_3)-COOH$$, which is 2-methylbut-2-enoic acid (also known as tiglic acid or $$\alpha,\beta$$-unsaturated acid).

Therefore, the correct answer is Option A.