Breakdown of Если в комнате душно, то я открываю форточку и выключаю обогреватель.
Questions & Answers about Если в комнате душно, то я открываю форточку и выключаю обогреватель.
Because в can take either the prepositional or the accusative, depending on meaning:
- в комнате = in the room (location, no movement) → prepositional
- в комнату = into the room (movement toward) → accusative
So in this sentence, the meaning is location: If it’s stuffy in the room..., so в комнате is correct.
Душно means something like stuffy, airless, or close in the sense of unpleasant warm air.
It is not a normal adjective here. It is a predicative adverb / category of state word, which is often used in impersonal sentences:
- Мне холодно. = I am cold.
- Здесь темно. = It is dark here.
- В комнате душно. = It is stuffy in the room.
Because of that, it does not change for gender, number, or case.