A teacher tells the students that it requires 2 cups of water, 3/4" cup of milk, 2 teaspoons each of sugar and tea powder to make two cups of tea. Then he asks students how many cups of milk is required to make 4 cups of tea. This example illustrates the concept of:

Correct option is D

The correct answer is option (d) Proportionality
The teacher is asking the students to determine how much milk is needed to make four cups of tea, given that two cups of tea require 3/4 cup of milk. This is an example of proportionality, as the amount of milk needed is proportional to the number of cups of tea.