Which of the following indicates the number of free -OH groups in an oil or fat

Options

A. Iodine value
B. Acid value
C. Acetyl value
D. Saponification value

Answer

To determine which value indicates the number of free -OH groups in an oil or fat, we need to analyze the given options: iodine value, acid value, acetylene value, and saponification value.

### Step-by-Step Solution:

1. **Understanding Iodine Value**:
- The iodine value measures the degree of unsaturation in fats and oils. It indicates how many double bonds are present in the fatty acid chains. However, it does not provide information about the number of free -OH groups.

**Hint**: Iodine value relates to unsaturation, not -OH groups.

2. **Understanding Acid Value**:
- The acid value is a measure of the free fatty acids in a fat or oil. It indicates the extent of hydrolysis and rancidity but does not directly indicate the number of free -OH groups.

**Hint**: Acid value relates to free fatty acids, not -OH groups.

3. **Understanding Acetylene Value**:
- The acetylene value is also related to the degree of unsaturation in fats and oils, similar to the iodine value. It does not provide information about the number of free -OH groups.

**Hint**: Acetylene value also relates to unsaturation, not -OH groups.

4. **Understanding Saponification Value**:
- The saponification value indicates the amount of base required to saponify a given quantity of fat or oil. This value is related to the total number of fatty acids and their chain lengths, which indirectly relates to the number of free -OH groups present in the glycerol backbone of triglycerides.

**Conclusion**: The saponification value is the correct answer, as it gives an indication of the number of free -OH groups in an oil or fat.

### Final Answer:
The saponification value indicates the number of free -OH groups in an oil or fat.