Breakdown of В моей чашке лежит пакетик чёрного чая, а в её кружке — пакетик зелёного.
Questions & Answers about В моей чашке лежит пакетик чёрного чая, а в её кружке — пакетик зелёного.
Because after в when it means in for a location, Russian normally uses the prepositional case.
So:
- чашка → в чашке
- кружка → в кружке
This is the same location pattern as:
- в доме = in the house
- в книге = in the book
- в комнате = in the room
If there were motion into something, Russian would usually use the accusative instead:
- в чашку = into the cup
- в кружку = into the mug
So here it is в моей чашке and в её кружке because the teabags are already there.
Because мой has to agree with the noun it describes in gender, number, and case.
The noun чашка is:
- feminine
- singular
- here in the prepositional case
So мой becomes моей.
Compare:
- моя чашка = my cup
- в моей чашке = in my cup
This is normal adjective/pronoun agreement in Russian.