Questions & Answers about Из окна виден мост.
- из – from/out of (preposition)
- окна – window in the genitive singular (of the window)
- виден – is visible / can be seen (short form of a passive participle/adjective)
- мост – bridge in the nominative singular (subject)
Very literally: “From (the) window is visible (the) bridge.”
In this sentence, мост is the grammatical subject: the bridge is visible (from the window).
- Russian structure: Из окна виден мост.
- Subject: мост (nominative)
- Predicate: виден (agrees with мост)
We are not saying “Someone sees the bridge” (which would use a verb like вижу and accusative). We are describing the state of the bridge: it is visible. So nominative is correct.