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 book of the Tamil language. It is part of the Sangam literature, which represents a golden era of Tamil culture and literary tradition.

2. Authorship and Structure: Written by the author Tolkappiyar, it is divided into three sections (called Adhikaram): Eluttadikaram (on letters/orthography), Solladikaram (on words/morphology-syntax), and Poruladikaram (on subject matter/poetics and linguistics). Each section consists of nine chapters.

3. Significance: It does not just outline grammar rules but also provides invaluable insights into the social, cultural, and political life of the Tamil people during the Sangam era. Therefore, it is a foundational classic of the Tamil language.