Which one of the following is a mordant ?

Options

A. Tannic acid
B. Metallic hydroxide
C. Salts of `Al , Cr , Fe , Sn`
D. All of these

Answer

To determine which one of the given options is a mordant, we need to understand what a mordant is and its role in dyeing processes.

### Step-by-Step Solution:

1. **Define Mordant**: A mordant is a substance used to set dyes on fabrics. It acts as a dye fixative, meaning it helps the dye adhere to the fabric.

2. **Function of Mordants**: Mordants work by forming a coordination complex with the dye, which then attaches to the fabric. This process enhances the intensity and durability of the dye on the material.

3. **Examples of Mordants**: Common mordants include metallic salts such as aluminum sulfate, iron(III) chloride, and tannic acid. These substances can interact with dyes to improve their binding to the fabric.

4. **Analyze Given Options**: If the question provides multiple choices, we need to evaluate each one to see if it fits the definition of a mordant.

- **Tannic Acid**: This is known to act as a mordant, particularly in dyeing cotton. It uses its hydroxyl (OH) groups to form hydrogen bonds with cellulose in the fabric.
- **Metallic Hydroxides**: These can also function as mordants in dyeing processes.
- **Metal Salts**: Many metal salts are recognized as effective mordants.

5. **Conclusion**: Based on the definitions and examples discussed, we can identify which option among the provided choices is a mordant.