What are the hispanic people found in california?

Mexicans                                   

This sentence is incorrect since the adjective must coincide in gender and number with the person to whom it refers, therefore the correct answer must be Mi abuelo es argentino.

Explanation:

Adjectives are those words that accompany the noun and which express a specific quality of them.

In this case, we have an example of what in Spanish is called the Adjetivo Gentilicio.

It is used to name the geographical origin of a noun. In this case, from grandfather (abuelo).

It is important that the adjective coincide in gender and number, so if the word grandfather is male, the adjective must also coincide.

This leads us to the correct answer is:

Mi abuelo es argentino.