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I found this reaction over here:

image

which illustrates the carbonyl test but looks fuzzy.

Assuming that the R in the product is a typo for H, I couldn't conserve the number of Nitrogen atoms.

What is the correct reaction?
Is this correct?
Is there a possibility of a methyl substitution on the ring in a variant of this test?

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Somebody messed up the scheme completely!

As you have already imagined, there is no magical $\ce{NO2}$ to $\ce{CH3}$ conversion in this classical reaction ;-)

formation of a dinitrophenylhydrazone

In the times before modern spectroscopy, these reactions were valuable analytical tools: the melting points of the dinitrophenylhydrazones and/or other derivatives were used to identify the carbonyl compounds.

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The methyl group on the product is an error. It should be a nitro group. Also you are right that the R group should be an H (or the other way around depending on what they intended). It looks like someone stuck two different images together but forgot to check to see if they matched up.

Other than that the reaction shown is correct. The reagent used in 2,4-dinitrophenylhydrazine, commonly know as DNPH.

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