Yes, at is a preposition.
The word 'of' is a PREPESITION.
A preposition is a word that shows the relationship between a noun (or pronoun) and other words in a sentence. Prepositions often indicate location, direction, time, or the relationship between two things. Example prepositions include "in," "on," "under," "over," and "between."
A preposition is a word used to show the relationship between a noun or pronoun and other words in a sentence. It is typically placed before a noun or pronoun to indicate time, place, direction, or other relationships.