Glucose on reaction with bromine water forms gluconic acid which confirms the presence of:

-CHO group

The correct answer is Option 2. -CHO group.

Let us dive into how the reaction of glucose with bromine water confirms the presence of the aldehyde group.

Glucose and Its Structure

Glucose is a six-carbon sugar (a hexose) with the molecular formula \(C_6H_{12}O_6\). It is an aldose, meaning it contains an aldehyde group \((-CHO)\) at one end of its carbon chain. Its structure can be represented as:

Here, the \(-CHO\) group is at the end of the molecule, making glucose an aldose sugar

Reaction with Bromine Water

Bromine water is a mild oxidizing agent. When glucose reacts with bromine water, it oxidizes the aldehyde group in glucose.
 Oxidation of the Aldehyde Group

The aldehyde group in glucose is oxidized to a carboxyl group (-COOH). This oxidation converts glucose into gluconic acid, which contains the carboxyl group at the end of the molecule. The molecular formula of gluconic acid is \(C_6H_{12}O_6\), which indicates the presence of a carboxyl group. This confirms that the original glucose molecule had an aldehyde group that was converted to a carboxyl group.

Confirming the Functional Group

Aldehyde Group (-CHO):

The reaction with bromine water specifically confirms the presence of the aldehyde group because only aldehydes react with bromine water to form acids (carboxyl groups). The aldehyde group is oxidized to a carboxyl group in gluconic acid.

Carboxyl Group (-COOH):

While gluconic acid contains a carboxyl group, the reaction confirms the presence of the aldehyde group in glucose, as it’s this group that gets oxidized.

Five -OH Groups:

Glucose does have five hydroxyl (-OH) groups, but the reaction with bromine water is used to confirm the presence of the aldehyde group, not the hydroxyl groups.

Ketonic Group:

Glucose does not contain a ketone group. The presence of the aldehyde group is specifically confirmed by this reaction.

Summary

The oxidation of glucose by bromine water converts the aldehyde group (-CHO) in glucose into a carboxyl group (-COOH) in gluconic acid. This reaction confirms the presence of the aldehyde group in glucose.

The correct answer is: CHO group.