Answer:

Nitrous acid (HNO2) can react with various organic compounds to form different products. In this case, we need to determine which compound, when reacted with nitrous acid followed by treatment with NaOH, produces a blue color.

Here are the given options:

A) RCH2NO2
B) R3CNO2
C) C6H5NO2
D) R2CHNO2

To identify the compound that produces a blue color, we need to consider the reaction mechanism and the nature of the resulting products.

Reaction Mechanism:
The reaction of nitrous acid (HNO2) with an organic compound involves the formation of a diazonium salt. This reaction is known as diazotization. Diazonium salts are unstable and can undergo different reactions depending on the conditions.

When a diazonium salt is treated with NaOH, it undergoes a reaction called diazo coupling. During this process, the diazonium salt reacts with a phenol or an aromatic amine to form an azo compound. Azo compounds are known for their vibrant colors, including blue.

Analysis of Options:
A) RCH2NO2 - This compound does not contain any aromatic or phenolic groups, so it is unlikely to produce a blue color during diazo coupling.

B) R3CNO2 - This compound is a nitroalkane, which is not expected to undergo diazotization or diazo coupling reactions.

C) C6H5NO2 - This compound is nitrobenzene, which contains both a nitro group and an aromatic ring. Nitrobenzene can undergo diazotization and subsequent diazo coupling reactions. Therefore, it is a potential candidate for producing a blue color.

D) R2CHNO2 - This compound does not contain any aromatic or phenolic groups, so it is unlikely to produce a blue color during diazo coupling.

Conclusion:
Based on the analysis, the compound that is most likely to produce a blue color when reacted with nitrous acid followed by treatment with NaOH is C6H5NO2 (nitrobenzene).