Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.

Category: elements 
Words: pay, cool, combustion, air, fire
pay

Category: physical activity 
Words: drop, fall, leaves, bend, exercise
leaves

Category: aesthetic characteristic 
Words: fair, medium, fine, pale, size

fine