Preparation of looking mirrors involves the use of :

Options

A. red lead
B. ammonical silver nitrate
C. ammonical `AgNO_(3)`+red lead
D. ammonical `AgNO_(3)`+red lead+HCHO

Answer

To solve the question regarding the preparation of looking mirrors, we need to understand the components involved in the process. The preparation of looking mirrors typically involves the following steps:

### Step-by-Step Solution:

1. **Identify the Components**:
The preparation of looking mirrors involves several chemicals. The key components mentioned are:
- Ammonical silver nitrate (AgNO3 in ammonia solution)
- Red lead (Pb3O4)
- Formaldehyde (HCHO)

2. **Role of Ammonical Silver Nitrate**:
Ammonical silver nitrate is used to produce silver oxide (Ag2O) when it reacts with sodium hydroxide (NaOH). The reaction is as follows:
\[ 2 \text{AgNO}_3 + 2 \text{NaOH} \rightarrow \text{Ag}_2\text{O} + 2 \text{NaNO}_3 + 2 \text{H}_2\text{O} \]
This silver oxide is essential for the subsequent reactions.

3. **Formation of Tollen's Reagent**:
The silver oxide (Ag2O) then reacts with sodium nitrate (NaNO3) and ammonia (NH3) to form Tollen's reagent:
\[ \text{Ag}_2\text{O} + 2 \text{NaNO}_3 + 4 \text{NH}_3 \rightarrow 2 \text{Ag(NH}_3\text{)}_2\text{NO}_3 + \text{NaOH} \]
Tollen's reagent is a solution of silver(I) complex that is used to test for aldehydes.

4. **Reaction with Formaldehyde**:
When formaldehyde (HCHO) is introduced, it reacts with Tollen's reagent, leading to the reduction of silver ions to metallic silver, which deposits on the surface, forming a mirror:
\[ \text{RCHO} + 2 \text{Ag(NH}_3\text{)}_2^+ \rightarrow \text{RCOOH} + 2 \text{Ag} + 2 \text{NH}_3 \]
This reaction is what creates the silver mirror effect.

5. **Function of Red Lead**:
Red lead (Pb3O4) is used to protect the thin layer of silver from scratches and damage. It is also a cost-effective and readily available material.

6. **Conclusion**:
Based on the above reactions and roles of each component, the correct answer to the question is:
**Ammonical silver nitrate + Red lead + HCHO** (Option 4).

### Final Answer:
The preparation of looking mirrors involves the use of ammonical silver nitrate, red lead, and formaldehyde (HCHO).

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