"The mosque is situated near the office." Here the word 'near' is being used as:

The correct answer is: Preposition. 
Near and Near to:
- দুটোই  prepositions হিসেবে ব্যবহৃত হয়। এছাড়া, Near মাঝে মাঝে Adjective হিসেবেও ব্যবহৃত হয়। 
- The preposition near (to) means ‘not far away in distance’. বাংলা অর্থ করলে দাঁড়ায়, খুব বেশি দূরে না, কাছেই এমন। 
- Near and near to mean the same, but near is more common: 
যেমন: My mother loves to sit near the fire at night.

Source: CLIFFS TOEFL