Criteria or Criterias?

 • One of the criterias for electing our leaders is to check if they are mentally balanced. 

There are nouns whose plurals are formed by changing the vowels, a process called vowel mutation, few examples are: 

 Man / women

 Goose / geese

 Tooth/teeth, etc

There are nouns with irregular plural, some of which usually have the last two or three letters affected. Examples of such words include: 

 Thesis : theses

 Stimulus : stimuli

 Criterion : criteria

 Tempo : tempi 

 Stadium : stadiums / stadia

 Crisis / crises, etc.

We should note that when the plurals of these nouns are used, our verbs and determiners should correspond with the plural nouns too.  Therefore, when the above sentence is corrected, we have: 

• One of the criteria for electing our leaders is to check if they are mentally balanced.