In Tollen's test, aldehydes

Options

A. Are oxidised to acids
B. Are reduced to alcohol
C. Neither reduced nor oxidised
D. Precipitate `Ag^(+)` as AgCl

Answer

### Step-by-Step Solution:

1. **Understanding Tollen's Test**: Tollen's test is a qualitative test used to distinguish between aldehydes and ketones. Aldehydes can be oxidized to carboxylic acids, while ketones cannot be oxidized by Tollen's reagent.

2. **Preparation of Tollen's Reagent**: Tollen's reagent is prepared by mixing silver nitrate (AgNO3) with sodium hydroxide (NaOH). This reaction produces a light brown precipitate of silver oxide (Ag2O) along with sodium nitrate (NaNO3) and water.

**Chemical Reaction**:
\[ 2 \text{AgNO}_3 + 2 \text{NaOH} \rightarrow \text{Ag}_2\text{O} + 2 \text{NaNO}_3 + 2 \text{H}_2\text{O} \]

3. **Formation of Diamine Silver Hydroxide**: The silver oxide (Ag2O) is then treated with ammonia (NH3) and water to form the Tollen's reagent, which is diamine silver hydroxide (Ag(NH3)2OH).

**Chemical Reaction**:
\[ \text{Ag}_2\text{O} + 4 \text{NH}_3 + 2 \text{H}_2\text{O} \rightarrow 2 \text{Ag(NH}_3)_2\text{OH} \]

4. **Reaction of Aldehyde with Tollen's Reagent**: When an aldehyde (RCHO) is added to Tollen's reagent, it gets oxidized to a carboxylic acid (RCOOH). During this process, the silver ions (Ag+) in the Tollen's reagent are reduced to metallic silver (Ag), which can deposit as a silver mirror on the walls of the test tube.

**Chemical Reaction**:
\[ \text{RCHO} + \text{Ag(NH}_3)_2^+ + \text{OH}^- \rightarrow \text{RCOOH} + 2 \text{Ag} + \text{NH}_3 + \text{H}_2\text{O} \]

5. **Conclusion**: In Tollen's test, aldehydes are oxidized to carboxylic acids, and the Tollen's reagent is reduced to metallic silver. This is why Tollen's test is also known as the "Silver Mirror Test".

### Final Answer:
In Tollen's test, aldehydes are oxidized to carboxylic acids.

---