Select the most appropriate option that can substitute the underlined word in the following sentence.
His flight departs in 5:00 pm.

The correct answer is at.

In English grammar, prepositions of time are used to indicate when something happens:

1. at is used for specific, precise times (e.g., at 5:00 pm, at midnight, at noon).

2. in is used for unspecific times during a day, month, season, or year (e.g., in the morning, in April, in 2024).

3. from is used to show a starting point in time, usually paired with "to" or "until" (e.g., from 9:00 am to 5:00 pm).

4. for is used to express a duration or length of time (e.g., for two hours).

Since "5:00 pm" is a precise time, the correct preposition to introduce it is at. Therefore, the underlined word "in" should be substituted with "at".

Corrected Sentence:
His flight departs at 5:00 pm.