Which one of the following compounds will give orange precipitate when treated with 2,4-dinitrophenyl hydrazine?

The $$\mathrm{2,4\text{-}DNP}$$ ($$\mathrm{2,4\text{-}dinitrophenylhydrazine}$$) test, also known as Brady’s Reagent test, is a qualitative chemical test used to detect the presence of a carbonyl group.

Carbonyl compounds such as aldehydes and ketones give a positive test.

How It Works:

1. The Reagent

$$\mathrm{2,4\text{-}DNP}$$ reacts with the carbonyl carbon $$\mathrm{(C=O)}$$ of aldehydes and ketones through a nucleophilic addition-elimination reaction.

$$\mathrm{R_2C=O + H_2N\text{-}NH\text{-}C_6H_3(NO_2)_2 \longrightarrow R_2C=NNH\text{-}C_6H_3(NO_2)_2 + H_2O}$$

2. The Result

The reaction produces a crystalline precipitate called a hydrazone derivative.

3. Visual Confirmation

A positive test is indicated by the formation of a yellow, orange, or red precipitate.

The only ketone/aldehyde is option D.