What is the incorrect pronoun in this sentence

My dog chased their tail.

Their is the incorrect answer

The incorrect pronoun in this sentence is their.

Explanation:

In this case, the function of their word is like a possessive adjective.

While it is not a pronoun, it is similar to a possessive pronoun.

The correct way to write the sentence would be: My dog chased its tail.

Unlike a pronoun, instead of replacing a noun, the possessive adjective functions as an adjective, and is placed before the noun it will modify.