The correct answer is C. Dinesh asked Rani whether she was going to the party the next day.
The sentence “Are you going to the party tomorrow, Rani?” is a direct question. It is a question that can be answered with a simple yes or no. The question is directed at Rani, and it asks her whether she is going to the party the next day.
Option A is incorrect because it uses the word “whether” instead of “if”. The word “whether” is used to introduce a choice between two or more things. In this case, there is only one thing that Rani is being asked about: whether she is going to the party.
Option B is incorrect because it uses the word “you” instead of “she”. The word “you” is used to refer to the person who is being spoken to. In this case, Dinesh is speaking to Rani, so he should use the word “she” to refer to her.
Option D is incorrect because it does not include the word “whether” or “if”. A direct question must include one of these words in order to be grammatically correct.