Final answer:
The appropriate interrogatory word is 'Dónde' and it is used to ask about the location or place of something.
Step-by-step explanation:
The appropriate interrogatory word to fill in the blank in the question '¿Dónde está el mejor restaurante mexicano?' is A) Dónde.
This interrogatory word is used to ask about the location or place of something. In this case, the question is asking 'Where is the best Mexican restaurant?'
For example, you could use this question to ask someone for recommendations or to find out the specific location of the best Mexican restaurant.
Learn more about Interrogative words in Spanish