Questions & Answers about В чае плавает кусочек лимона.
Because в here means in, showing location, and after в with location Russian uses the prepositional case.
- dictionary form: чай = tea
- prepositional singular: чае
- so в чае = in the tea
This is a very common pattern:
- в доме = in the house
- в книге = in the book
- в чае = in the tea
Russian word order is flexible, so starting with В чае sets the scene first: as for the tea / in the tea...
So the sentence structure is roughly:
- В чае = in the tea
- плавает = is floating
- кусочек лимона = a small piece of lemon
This word order sounds natural when you first mention the location and then say what is there. English often does the same in a more limited way: In the tea, there is a piece of lemon floating.