Incorrect statement among the following is:

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1. **FeCl₃ Test:** Neutral Ferric Chloride ($FeCl_3$) is indeed used to detect phenols. It reacts with phenols to give a violet-coloured complex.
2. **Fehling's Solution:** This is a standard test for reducing sugars like glucose. It oxidizes glucose, and in the process, the copper(II) ions are reduced to a red precipitate of copper(I) oxide ($Cu_2O$).
3. **Tollen's Reagent:** Tollen's reagent (Ammoniacal Silver Nitrate) is used to detect **aldehydes** (which reduce it to metallic silver, forming a 'silver mirror'), not unsaturation. **Unsaturation** (double/triple bonds) is detected using **Bromine water** (which gets decolourised)  or **Baeyer's reagent** (alkaline $KMnO_4$, which gets decolourised) .
4. **NaHSO₃ Test:** Sodium hydrogen sulphite ($NaHSO_3$) forms crystalline addition products with aldehydes and ketones (carbonyl compounds), which is used for their separation and purification.

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