Questions & Answers about V pokoji jsou různé rekvizity.
Because the preposition v normally requires the locative case when it means in a place.
- base form: pokoj = room
- after v: v pokoji = in the room
So this is a case change, not a different word.
Here v means in.
So:
- v pokoji = in the room
In Czech, short prepositions like v, na, do, z are very common, and each one usually goes with a particular case. In this sentence, v is used for location, so it takes the locative.