Glycerol is added to soap. It functions-

Options

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

Explanation

**Step-by-Step Solution:**

1. **Understanding the Role of Glycerol in Soap:**
- Glycerol is a common additive in soap formulations. It is important to identify its primary function in this context.

2. **Analyzing the Options:**
- The options provided are:
1. As a filter
2. To increase lathering
3. To prevent rapid drying
4. To make soap granules

3. **Evaluating Each Option:**
- **Option 1 (As a filter):** Glycerol does not function as a filter in soap. Filters are typically substances that remove impurities or particles from a solution.
- **Option 2 (To increase lathering):** While lathering is an important property of soap, glycerol is not the primary agent for increasing lather. Instead, substances like gum rosin are used to enhance lathering.
- **Option 3 (To prevent rapid drying):** Glycerol is known for its humectant properties, which means it helps retain moisture. This is particularly useful in shaving soaps to prevent them from drying out too quickly.
- **Option 4 (To make soap granules):** Soap granules are typically formed from dried soap bubbles and do not require glycerol for their formation.

4. **Conclusion:**
- After evaluating all options, the correct answer is **Option 3: To prevent rapid drying**. Glycerol is added to soap primarily for this purpose.