Formalin is an aqueous solution of

Options

A. fluorescein
B. Formic acid
C. formaldehyde
D. furfuraldehdye

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks what formalin is an aqueous solution of.

2. **Define Formalin**: Formalin is commonly known as a 40% solution of formaldehyde in water.

3. **Composition of Formalin**:
- Formalin consists of approximately 40% formaldehyde.
- It also contains about 8% methanol.
- The remaining 52% is water.

4. **Conclusion**: Therefore, formalin is an aqueous solution of formaldehyde.

5. **Uses of Formalin**:
- It is used for preserving biological specimens.
- It acts as a disinfectant.
- It is also used in products like hardness and nail varnish.

6. **Final Answer**: Formalin is an aqueous solution of formaldehyde.

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