Answer:
The best option is indeed letter B. Rajeet opened the window; he loved the smell of the rainstorm.
Step-by-step explanation:
We have what is called a run-on sentence when independent clauses are joined incorrectly. An independent clause is a group of words that makes sense on its own, without the help of another sentence. It already offers complete information.
If we join independent clauses without any sort of punctuation, we have a fused sentence. That is the sentence presented in the question. Many people would be tempted to place a comma between them, but that would only create a comma splice if we don't add a proper conjunction. The alternative then is to place a semicolon between the two independent sentences. The punctuation would be considered correct and there would be no need to add a conjunction. Thus, the sentence would be:
Rajeet opened the window; he loved the smell of the rainstorm.