Which of the following is incorrect

Options

A. `FeCI_(3)` is used in the detection of phenols
B. Fehling's solution is used in the detection of glucose
C. Tollen's reagent is used in detection of unsaturation
D. `NaHSO_(3)` is used in the detection of carbonyl compounds

Answer

To determine which of the following statements is incorrect, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Evaluate Option 1:**
- Statement: "FeCl3 is used in the detection of phenols."
- Explanation: This statement is correct. When phenols react with neutral FeCl3, they form a complex that gives a violet coloration, indicating the presence of phenolic compounds.

2. **Evaluate Option 2:**
- Statement: "Fehling's solution is used in the detection of glucose."
- Explanation: This statement is also correct. Glucose contains an aldehyde group, and Fehling's solution is used to detect aldehydes. When glucose is present, it reduces the copper(II) ions in Fehling's solution to copper(I) oxide, resulting in a brick-red precipitate.

3. **Evaluate Option 3:**
- Statement: "Tollens' reagent is used in detection of unsaturation."
- Explanation: This statement is incorrect. Tollens' reagent is actually used to detect aldehydes, not unsaturation. The correct tests for unsaturation include bromine water or dilute KMnO4, which can indicate the presence of double or triple bonds.

4. **Evaluate Option 4:**
- Statement: "NaHSO3 is used in detection of carbonyl compounds."
- Explanation: This statement is correct. Sodium bisulfite (NaHSO3) reacts with carbonyl compounds (especially aldehydes) to form bisulfite adducts, which can be used for identification. Ketones can also react, but the reaction is more favorable with aldehydes.

### Conclusion:
- The incorrect statement is **Option 3**, as it misrepresents the use of Tollens' reagent.