Final answer:
In the sentence provided, 'everyone' is used as a pronoun to collectively refer to all the people present and to avoid repetition.
Step-by-step explanation:
In the sentence 'Kai threw a star at Brandon while Mr. Morton was writing on the board and everyone laughed,' the word 'everyone' functions as a pronoun. A pronoun is a word used in place of a noun, often to avoid repetition and to help sentences sound more natural.
In this case, 'everyone' is standing in for all the people present in the situation described. It replaces the repeated use of writing out all the names of the individuals who laughed and serves as a collective noun to refer to them as a group. Thus, in this context, 'everyone' is a pronoun rather than a noun.