The presence of -CHO group in glucose is confirmed by its:

Options

A. reaction with `PCl_(5)`
B. reaction by Na-Hg to give S-orbital
C. reaction with Fehling solution
D. reaction with Tollen's reagent

Answer

To confirm the presence of the -CHO (aldehyde) group in glucose, we can analyze the reactions that glucose undergoes with specific reagents. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understanding the Structure of Glucose
- Glucose is an aldohexose, which means it has an aldehyde group (-CHO) at one end of its carbon chain.
- The structure can be represented as follows:
\[ \text{CHO - CH}_2\text{OH - CH(OH) - CH(OH) - CH(OH) - CH}_2\text{OH} \]

### Step 2: Reaction with PCl5
- When glucose reacts with phosphorus pentachloride (PCl5), it forms a geminal dihalide, specifically a geminal chloride.
- However, this reaction does not specifically confirm the presence of the aldehyde group since it does not lead to a definitive identification of the -CHO group.

### Step 3: Reaction with NaBH4
- Sodium borohydride (NaBH4) is a reducing agent that can reduce aldehydes to alcohols.
- When glucose reacts with NaBH4, the aldehyde group (-CHO) is reduced to a primary alcohol (-CH2OH), forming sorbitol.
- The reaction can be represented as:
\[ \text{CHO} + \text{NaBH}_4 \rightarrow \text{CH}_2\text{OH (Sorbitol)} \]
- This confirms the presence of the aldehyde group because the reduction only occurs if the aldehyde is present.

### Step 4: Reaction with Tollens' Reagent and Fehling's Solution
- Both Tollens' reagent and Fehling's solution are used to test for aldehydes.
- In the presence of glucose, these reagents will oxidize the aldehyde group:
- Tollens' reagent (AgNO3 in NH3) produces a silver mirror.
- Fehling's solution (CuSO4 in alkaline solution) produces a red precipitate of copper(I) oxide.
- The positive results from these tests also confirm the presence of the aldehyde group in glucose.

### Conclusion
- The presence of the -CHO group in glucose is confirmed by its reaction with NaBH4 to form sorbitol, as well as by the positive results from Tollens' reagent and Fehling's solution.

### Final Answer
The presence of -CHO group in glucose is confirmed by its reaction with NaBH4 (to form sorbitol) and by positive tests with Tollens' reagent and Fehling's solution.