To identify the correct sentence, we must understand the correct usage of the preposition "opposite". The word "opposite" typically doesn't require additional prepositions such as "to", "from", or "of". Therefore:
The office is opposite to the bank. - Incorrect. The use of "to" is redundant.
The office is opposite the bank. - Correct. This is the standard usage without any extra prepositions.
The office is opposite from the bank. - Incorrect. "From" is not needed here.
The office is opposite of the bank. - Incorrect. The use of "of" is unnecessary.
Thus, the grammatically correct sentence is: The office is opposite the bank.