Which dietary standard values vary with calorie intake?

The answer is fat.
(Assuming the options of this exercise are fat, iron, calcium, vitamin C)

There are three type of nutrients that can change our calorie intake: carbohydrates, proteins and fats. These are the nutrients that give us energy.

Carbohydrates and proteins have 4 calories per each gram, and fatty acids have 9 calories per each gram, being the nutrient with the highest number of calories.
Other nutrients such as vitamins (vitamin C), minerals(iron,calcium) don't have calories so they don't interfere with calorie intake.