The correct answer is: C. Unsaturation in oil.
Iodine value is a measure of the degree of unsaturation of an oil or fat. It is determined by the number of grams of iodine that are absorbed by 100 grams of the oil or fat. The higher the iodine value, the more unsaturated the oil or fat is.
Unsaturated oils and fats are liquid at room temperature, while saturated oils and fats are solid. Unsaturated oils and fats are also more susceptible to oxidation than saturated oils and fats.
Iodine value is used to determine the quality of an oil or fat. For example, it is used to determine the freshness of fish oil. It is also used to determine the suitability of an oil or fat for use in certain applications, such as in the manufacture of soaps and detergents.
Hydroxyl groups, alkali content, and carboxylic groups are not directly related to the iodine value of an oil or fat.