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 analyze the components involved in the process. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Components
Looking mirrors are typically prepared using specific chemical reagents. The options provided include:
1. Red lead
2. Ammonical silver nitrate
3. Ammonical silver nitrate plus red lead
4. Ammonical silver nitrate plus red lead plus formaldehyde

### Step 2: Understand the Role of Ammonical Silver Nitrate
Ammonical silver nitrate is a key reagent in the preparation of looking mirrors. It is known for its ability to produce a silver mirror through a reduction reaction.

### Step 3: Reaction Mechanism
The preparation involves a series of reactions:
1. **Formation of Silver Oxide**: Ammonical silver nitrate reacts with a base (like NaOH) to form silver oxide (Ag2O).
\[ \text{AgNO}_3 + \text{NaOH} \rightarrow \text{Ag}_2\text{O} + \text{NaNO}_3 + \text{H}_2\text{O} \]

2. **Formation of Tollens' Reagent**: The silver oxide then reacts with ammonia to form Tollens' reagent, which is a complex of silver.
\[ \text{Ag}_2\text{O} + 2\text{NH}_3 \rightarrow 2\text{Ag(NH}_3)_2\text{NO}_3 + \text{NaOH} \]

### Step 4: Reaction with Formaldehyde
Formaldehyde (HCHO) is then used in the reaction with Tollens' reagent. Aldehydes reduce Tollens' reagent, resulting in the deposition of metallic silver, which forms the mirror.
\[ \text{HCHO} + 2\text{Ag(NH}_3)_2\text{NO}_3 \rightarrow \text{Ag (s)} + \text{other products} \]

### Step 5: Role of Red Lead
Red lead (Pb3O4) is used in the process to protect the thin layer of silver from scratches and damage, ensuring the durability of the mirror.

### Conclusion
Based on the analysis, the preparation of looking mirrors involves the use of:
- Ammonical silver nitrate
- Red lead
- Formaldehyde

Thus, the correct answer is option four: **Ammonical silver nitrate plus red lead plus formaldehyde**.