Analyze Statement I

Aldol reaction occurs in aldehydes/ketones having at least one $\alpha$-hydrogen.

• The $\alpha$-hydrogen is relatively acidic because removal of this proton gives an enolate ion.
• This enolate is resonance stabilized.
• The enolate then attacks another carbonyl compound, leading to the aldol product.

Therefore, the acidity of $\alpha$-hydrogens is indeed responsible for the aldol reaction.

So, Statement I is correct.

Analyze Statement II

Statement II says:

Reaction between benzaldehyde and ethanal will NOT give Cross-Aldol product.

Let us check:

• Benzaldehyde: $\mathrm{C_6H_5CHO}$ has no $\alpha$-hydrogen.
• Ethanal: $\mathrm{CH_3CHO}$ has $\alpha$-hydrogens.

In a crossed aldol reaction, if one carbonyl compound has no $\alpha$-hydrogen and the other has $\alpha$-hydrogen, the reaction proceeds cleanly because only one can form the enolate.

Hence, ethanal forms the enolate, which attacks benzaldehyde, giving a cross-aldol product.

This is actually the classic Claisen–Schmidt type crossed aldol condensation situation.

Therefore, the statement that it will NOT give cross-aldol product is incorrect.

So, Statement II is incorrect.

Choose the correct option

• Statement I: Correct
• Statement II: Incorrect

Therefore, the correct option is:

$\boxed{\text{B}}$

Comparison with stored answer

Stored correct answer = B

My derived answer = B

They match.