The reference value that is expressed as a percentage of total calories is called

The reference value that is expressed as a percentage of total calories is called as % daily value.

Explanation:

The % daily value tells about the the nutrients which are present in a single serving of food. They are mostly present on the Nutritional Fact Label for foods. The standard for the % daily value is set to  2000 calorie. 2000 calories are required for a healthy adult diet. But even if a person has a calorie uptake lower or higher then that, he/she can still use the % Daily Value  as a guideline.

For example, If 2% vitamin C is written on a label than it defines that one serving of that product supplies 2% of the vitamin C that you require each day.

c. is the correct answer