Fill in the blank by choosing the appropriate word/words from those given in the brackets.
(acetaldehyde, formaldehyde, benzaldehyde, yellow, white, violet, Cannizzaro's, Liebermann, no `alpha`-hydrogen atom, `1alpha`-hydrogen atom, `2alpha`-hydrogen atoms, aldol, `beta`-hydroxy aldehyde, aldol condensation, mixed condensation, + I,-I, -M,+ M. decreases, increases, benzalchloride, PCI, SOCh. sec, alcohol, tert, alcohol, phenylhydrozone, semicarbazone, more, less, acetals, ketals, silver mirror, test, urotropine, acetaldehyde cyanohydrin, lactic acid, benzoic acid, Sodalime, ethanoic acid, propanoic acid, electrolysis, Kolbe's electrolytic reaction, carbon dioxide, water, amides, alpha, halogen, phosphorus, weaker, stronger, ethyl alcohol, dibasic,monobasic, 2,2-dimethylpropanoic acid, `CH_(3)COCI`, acetic acid, `CH_(3)CH_(2)CH_(2)COOK`, enatiomers, diastereo, `K_(a)` `pk_(a)`, methanoic acid, higher, lower.)
All aldehydes and ketones react with phenylhydrazine in presence of an acid to form........

Explanation

To solve the question, we need to fill in the blank with the correct term that describes the product formed when aldehydes and ketones react with phenylhydrazine in the presence of an acid.

### Step-by-Step Solution:

1. **Understanding the Reaction**: Aldehydes and ketones react with phenylhydrazine to form a specific type of compound. This reaction is a well-known method in organic chemistry used to identify aldehydes and ketones.

2. **Identifying the Product**: The product formed from the reaction of an aldehyde or a ketone with phenylhydrazine is called a phenylhydrazone. This is because the phenylhydrazine (which contains the phenyl group and hydrazine) reacts with the carbonyl group (C=O) of the aldehyde or ketone.

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