Topic: verb (ক্রিয়া),

Best Answer Explained in Below-:

In the sentence "I am in class twelve," the word "am" serves as a **principal verb**. A principal verb conveys the main action or state of being in a sentence. In this case, "am" functions as a linking verb, connecting the subject "I" with the subject complement "in class twelve," which describes the state of being of the subject.

The options provided each refer to different roles that verbs can play:

- A **cognate verb** typically relates to verbs derived from the same root or base as another verb, not applicable here.
- A **principal verb** directly expresses the main action or state; in this sentence, it describes the existence or condition of "I."
- An **auxiliary verb**, or helping verb, assists the main verb in expressing its tense, mood, or voice (e.g., "is" in "He is running"), but "am" in this instance stands alone in its role.
- A **factitive verb** indicates a result of an action or leads to a transformation, but this does not apply to the state being expressed.

Thus, "am" is correctly identified as a principal verb, as it defines the state of the subject without the need for another verb's support.