The following sentence has been divided into four segments. Identify the segment that contains a grammatical error.
My students are / waiting for / their flights / at the gate no. 6.

The correct answer is: at the gate no. 6.

Detailed Explanation:

In English grammar, when a noun is followed by a specific number or letter that identifies it (such as gate numbers, room numbers, platform numbers, page numbers, etc.), we do not use the definite article 'the' before the noun.

For example:

• Correct: at Gate 6 or at Gate No. 6

• Incorrect: at the gate no. 6

Therefore, the segment "at the gate no. 6." contains a grammatical error. The word 'the' should be omitted to make the sentence grammatically correct: "My students are waiting for their flights at Gate No. 6."