Identify what “carbolic acid” means

Carbolic acid is the common name for phenol, i.e. $\mathrm{C_6H_5OH}$.

Check each option for hydrolysis

Option A: Cumene

Cumene is isopropyl benzene, $\mathrm{C_6H_5CH(CH_3)_2}$.

• On oxidation, cumene gives cumene hydroperoxide, which on acid cleavage gives phenol.
• But simple hydrolysis of cumene does not give phenol.

So, A is incorrect.

Option B: Benzenediazonium chloride

Benzenediazonium chloride is $\mathrm{C_6H_5N_2^+Cl^-}$.

On hydrolysis (usually warming with water):

This directly gives phenol (carbolic acid).

So, B is correct.

Option C: Benzal chloride

Benzal chloride is $\mathrm{C_6H_5CHCl_2}$.

Gem-dihalides on hydrolysis form carbonyl compounds. Thus:

Product is benzaldehyde, not phenol.

So, C is incorrect.

Option D: Ethylene glycol ketal

Ketals on hydrolysis regenerate the parent carbonyl compound and ethylene glycol.

They do not give phenol.

So, D is incorrect.

Final conclusion

The compound whose hydrolysis gives carbolic acid (phenol) is:

Comparison with stored correct answer

Stored correct answer = B.

My derived answer also = B, so they agree.