Which of the following is used as indelible ink

Options

A. Aq. `CuSO_(4)` solution
B. Aq. `AgNO_(3)` solution
C. Aq. `NaCl` solution
D. Aq. `NaOH` solution

Explanation

To determine which compound is used as indelible ink, we need to analyze the options provided and identify the correct one based on the information given in the video transcript.

### Step-by-Step Solution:

1. **Understanding Indelible Ink**: Indelible ink is a type of ink that cannot be easily removed, which is often used in elections to mark voters.

2. **Analyzing the Options**:
- **Option 1: Aqueous CuSO4 solution** - Copper(II) sulfate is not known for use as indelible ink.
- **Option 2: Aqueous AgNO3 solution** - Silver nitrate is commonly used as indelible ink due to its staining properties.
- **Option 3: Aqueous NaCl solution** - Sodium chloride is common table salt and does not have properties suitable for indelible ink.
- **Option 4: Aqueous NaOH solution** - Sodium hydroxide is a strong base and is not used for indelible ink.

3. **Identifying the Correct Answer**: Based on the analysis, the only option that is used as indelible ink is **Option 2: Aqueous AgNO3 solution (Silver Nitrate)**.

4. **Concentration of Silver Nitrate**: The transcript mentions that silver nitrate is used in concentrations ranging from 10% to 18% for indelible ink.

### Final Answer:
The compound used as indelible ink is **Aqueous AgNO3 solution (Silver Nitrate)**.

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