Which one of the following undergoes reaction with 50% sodium hydroxide solution to give the corresponding alcohol and acid? 

Benzaldehyde 

The correct answer is option 2. Benzaldehyde.

Benzaldehyde undergoes reaction with 50% sodium hydroxide solution to give the corresponding alcohol and acid. This reaction is known as the Cannizzaro reaction, which occurs with aldehydes that lack alpha hydrogen atoms.

Here is a brief overview of the Cannizzaro reaction:

Benzaldehyde reacts with concentrated sodium hydroxide (50%) solution. In this reaction, one molecule of benzaldehyde is reduced to benzyl alcohol, and another molecule is oxidized to benzoic acid.

The reaction can be summarized as follows:

So, the correct answer is Benzaldehyde.