* Objects are the things that prepositions describe the relationship of. For example, in the sentence "The cat is *under* the table," "table" is the object of the preposition "under."
* Prepositions are words that show the relationship between a noun or pronoun and another word in the sentence. Common prepositions include "on," "in," "under," "over," "to," "from," etc.
So, the answer to your question is: Neither.
The question asks for a word that represents both an object and a preposition. This is like asking for a word that is both a dog and a cat - it's impossible!
Words can be objects of prepositions, but they cannot be prepositions themselves.