Choose the sentence that has the correct preposition in it:

The correct option is: Radha will not be able to reach within half an hour.

Step-by-step Explanation:
Prepositions are words used before nouns or pronouns to show direction, time, place, location, or spatial relationships. Let us analyze each option to understand the usage of prepositions:

1. "Radha will not be able to reach within half an hour." (Correct)
Here, the preposition "within" is used correctly. "Within" means "inside the limits of" or "before the end of" a specified period of time. In this context, it correctly indicates that Radha cannot reach her destination before thirty minutes have elapsed.

2. "They will return with fifteen minutes." (Incorrect)
The preposition "with" means accompanied by or possessing. In this sentence, it is used incorrectly to show a time limit. The correct preposition should be "within" (They will return within fifteen minutes) or "in" (They will return in fifteen minutes).

3. "The students came onto the classroom." (Incorrect)
The preposition "onto" indicates movement to a position on the surface of something (e.g., jumping onto a table). Since a classroom is an enclosed three-dimensional space, the correct preposition to show movement entering it is "into" (The students came into the classroom).

4. "Susheel works on the office every weekend." (Incorrect)
The preposition "on" refers to a position on a surface. Since an office is a physical building or enclosed workspace, the correct preposition is "in" (Susheel works in the office) or "at" (Susheel works at the office).