\('A' + H_2O/H^+ \longrightarrow 'B' + NaOH + CaO \longrightarrow \text{ Benzene}\)

The compound \('A'\) is

Benzamide

The correct answer is option 4. Benzamide.

Let us analyze the given reaction steps:

1. \( 'A' + H_2O/H^+ \longrightarrow 'B' \)

This step involves the conversion of compound \( 'A' \) to compound \( 'B' \) under acidic conditions with the addition of water.

2. \( 'B' + NaOH + CaO \longrightarrow \text{Benzene} \)

In this step, compound \( 'B' \) is converted to benzene by treatment with sodium hydroxide (\( NaOH \)) and calcium oxide (\( CaO \)).

Given that the final product is benzene, compound \( 'B' \) must be a precursor or derivative that can be converted to benzene.

Now, let's analyze the options provided:

1. Aniline: Aniline is a primary aromatic amine (\( C_6H_5NH_2 \)) and cannot directly be converted to benzene through the given reaction steps.

2. Acetanilide: Acetanilide (\( C_6H_5NHCOCH_3 \)) is also an amide derivative of aniline and cannot directly be converted to benzene through the given reaction steps.

3. Benzylchloride: Benzyl chloride (\( C_6H_5CH_2Cl \)) is an organic compound but does not contain a benzene ring in its structure.

4. Benzamide: Benzamide (\( C_6H_5CONH_2 \)) is an amide derivative of benzoic acid. Under acidic conditions, benzamide can undergo hydrolysis to yield benzoic acid, which could be further decarboxylated to form benzene. Therefore, compound \( 'A' \) is most likely Benzamide (option 4).

Thus, the compound \( 'A' \) is Benzamide.