Step 1: Understand the saponification value.
The saponification value is a measure of the amount of base (usually \( \text{NaOH} \)) required to hydrolyze a given quantity of fat or oil. It is expressed as the number of milligrams of KOH required to saponify 1 gram of fat or oil.
Step 2: Analyze the options.
- (1) \( \text{NH}_4\text{OH} \): Ammonium hydroxide is not used in saponification reactions.
- (2) \( \text{NaOH} \): This is the correct base used in the saponification reaction to hydrolyze fats or oils.
- (3) \( \text{C}_6\text{H}_5\text{OH} \): This is phenol, which is not used in the saponification reaction.
- (4) \( \text{KOH} \): Potassium hydroxide is another base that can be used, but sodium hydroxide is more commonly used for saponification value measurement.
Step 3: Conclusion.
The correct answer is (2), \( \text{NaOH} \), as it is the base commonly used to measure the saponification value.