Tolkappiyam is a book of grammar and poetics written in the_____ language

The correct option is Tamil.

Step-by-step Explanation:

1. Understanding Tolkappiyam: Tolkappiyam is the most ancient extant work of literature and the oldest surviving grammar text in the Tamil language.
2. Historical Context: It is attributed to the author Tolkappiyar and is believed to have been composed during the Sangam period, which is a golden age in the history of South Indian literature.
3. Scope of the Book: The text is divided into three sections: Ezhuttadikaram (which deals with orthography and phonology), Solladikaram (which deals with morphology and syntax), and Poruladikaram (which deals with the subject matter of literature, poetics, and rhetoric, detailing the life and conventions of ancient Tamil society).
4. Conclusion: Therefore, Tolkappiyam is a comprehensive work of grammar and poetics written specifically in the Tamil language.