Glycerol is added to soap. It function:

Options

A. as a filler
B. to increase lathering
C. to prevent rapid drying
D. to make soap granules

Explanation

To answer the question regarding the function of glycerol when added to soap, we can break down the information step by step.

### Step-by-Step Solution:

1. **Understanding Soap Composition**:
- Soap is typically made from the sodium or potassium salts of long-chain carboxylic acids. This structure gives soap its unique properties, allowing it to interact with both water and oils.

2. **Cleaning Action of Soap**:
- The cleaning action of soap is based on its dual nature. The long hydrocarbon chain of the soap molecule is hydrophobic (repels water) and dissolves in oils (which are often the main component of dirt). The ionic end of the soap molecule is hydrophilic (attracts water) and dissolves in water.

3. **Role of Glycerol**:
- Glycerol is known as a humectant, which means it has the ability to attract and retain moisture. This property is particularly beneficial in skin care products.

4. **Preventing Drying**:
- When glycerol is added to soap, it helps to prevent the skin from drying out. This is important because while soap cleans effectively, it can also strip away natural oils from the skin, leading to dryness.

5. **Conclusion**:
- Therefore, the primary function of glycerol in soap is to prevent rapid drying of the skin. This aligns with option C from the provided choices.

### Final Answer:
The function of glycerol when added to soap is to **prevent rapid drying** of the skin.

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