Questions & Answers about Ta melodia jest spokojna.
Because adjectives in Polish have to agree with the noun they describe.
Since melodia is:
- singular
- feminine
the adjective also has to be:
- singular
- feminine
So you get:
Here, spokojna matches melodia.
It is in the nominative case because it is the subject of the sentence.
In Ta melodia jest spokojna:
- ta melodia = the thing being talked about
- jest spokojna = what is being said about it
The adjective spokojna is also in the nominative here, because it is a predicate adjective after jest.