In the following question, a sentence is divided into four parts. Choose the part of the sentence which may contain a grammatical error in it. If all the parts of the sentence are grammatically correct and contextually meaningful, choose option “No error” as the answer choice.
One of the students (A)/ have failed (B)/ in the examination (C)/ this year. (D)

The correct option is B.

Let's analyze the sentence step-by-step to find the grammatical error:
The sentence is: "One of the students (A)/ have failed (B)/ in the examination (C)/ this year. (D)"

1. Subject-Verb Agreement:
The subject of the sentence is the pronoun phrase "One of the students". Here, the head word of the subject is "One", which is singular. The prepositional phrase "of the students" acts as a modifier and does not change the number of the subject.
Since the subject "One" is singular, it requires a singular verb to maintain subject-verb agreement.

2. Error Identification:
In part (B), the auxiliary verb used is "have" (plural), which is paired with the past participle "failed" to form the present perfect tense.
Since the subject is the singular pronoun "One", the auxiliary verb must be the singular "has" instead of the plural "have".

3. Correction:
The grammatically correct sentence should be: "One of the students has failed in the examination this year."
Therefore, the grammatical error is in part B.