Assertion: 2,2-Dimethylpropanal undergoes Cannizzaro reaction with concentrated NaOH.

Reason: Cannizzaro reaction is a disproportionation reaction. 

Both Assertion and Reason are correct but the Reason is not the correct explanation for the Assertion.

The correct answer is option 2. Both Assertion and Reason are correct but the Reason is not the correct explanation for the Assertion.

Assertion: 2,2-Dimethylpropanal undergoes Cannizzaro reaction with concentrated NaOH.

Cannizzaro Reaction: This reaction occurs with aldehydes that lack alpha-hydrogen atoms. In the presence of a strong base, such as concentrated NaOH, one molecule of the aldehyde is reduced to an alcohol, and another molecule is oxidized to a carboxylic acid. The structure of 2,2-dimethylpropanal is:

In 2,2-dimethylpropanal, there are no alpha-hydrogen atoms (hydrogen atoms attached to the carbon adjacent to the carbonyl group). This lack of alpha-hydrogens makes it a suitable candidate for the Cannizzaro reaction.

The assertion that 2,2-dimethylpropanal undergoes the Cannizzaro reaction with concentrated NaOH is correct because 2,2-dimethylpropanal lacks alpha-hydrogen atoms, making it a suitable candidate for this reaction.

Reason: Cannizzaro reaction is a disproportionation reaction.

Disproportionation Reaction: A reaction in which a single reactant is both oxidized and reduced, forming two different products. In the Cannizzaro reaction, one aldehyde molecule is reduced to an alcohol, while another is oxidized to a carboxylic acid.

The reason is also correct in describing the nature of the Cannizzaro reaction as a disproportionation reaction. However, this reason does not directly explain why 2,2-dimethylpropanal undergoes the reaction. The key to understanding why 2,2-dimethylpropanal undergoes the Cannizzaro reaction is the absence of alpha-hydrogen atoms, which is not mentioned in the reason.

While both the assertion and the reason are correct, the reason does not specifically explain why 2,2-dimethylpropanal undergoes the Cannizzaro reaction. The absence of alpha-hydrogen atoms in 2,2-dimethylpropanal is the crucial factor enabling it to undergo the Cannizzaro reaction.

Therefore, the correct answer is: Both Assertion and Reason are correct but the Reason is not the correct explanation for the Assertion.