Given below are four sentences, out of which one sentence is grammatically incorrect. Choose the option which points out the grammatically incorrect sentence. If all the sentences are correct, then choose ‘No error’ as the answer.

The correct option pointing out the grammatically incorrect sentence is: "She requested him that he should explain the procedure again."

Explanation and Analysis:

1. Grammar Rule for "Request":
When using the verb "request" in reporting speech or expressing a command/wish, it generally takes a direct object followed by an infinitive (to-infinitive), e.g., "She requested him to explain the procedure again."
Alternatively, if a that-clause is used, it should be followed by a subjunctive verb form or base verb without "should" (e.g., "She requested that he explain the procedure again"). Combining an object ("him") with a that-clause containing "should" ("requested him that he should...") is redundant and grammatically incorrect in modern standard English.

2. Analysis of other sentences:
• "The constable asked the visitors to wait outside the gate." – Correct structure (ask + object + to-infinitive).
• "The luggage was checked thoroughly before boarding the train." – Correct passive voice sentence.
• "He arrived on time and took his seat without any delay." – Correct sentence with appropriate prepositions and past tense consistency.

Therefore, the sentence containing the grammatical error is "She requested him that he should explain the procedure again."