English question about usage of prepositions with a conjunction?

I am wondering about the below sentences:

1. Where are you? – in London or In New York vs In London or New York.

2. Where are you? – in the office or at home?

Do I need to use a separate preposition before and after “or”? – if so, it’s okay.

Or

does only one preposition work? – if that’s the case, then it cannot be applied to the second sentence because we cannot say “in home”.

Thanks in advance.