"Do you have lemons?"
Translation:У вас є лимони?
Ukrainian nouns have several forms called cases.
Лимо́н is nominative singular (‘lemon’), лимо́ни is nominative plural (‘lemons’). Nominative case is used for the grammatical subject of the sentence, someone or something doing the action, or ‘being’. E.g. «Лимо́н додає́ ча́ю ки́слий сма́к» ‘A lemon adds a sour taste to the tea’. The ‘lemon’ does the action of ‘adding’, so it’s the subject, and this is why you use the nominative case.
Лимо́ном is instrumental singular. It’s usually translated ‘with/using lemon’, and it is used to describe the instrument through which something is done. For example: Окса́на зро́била чай кислі́шим лимо́ном ‘Oksana made the tea more sour with/using the lemon’. It’s also the case used after the preposition «з» ‘with, together with’: «з лимо́ном» ‘with lemon’, for example: чай з лимо́ном ‘tea with lemon’.
Note that this sentence’s structure of ‘Do you have lemons?’ is different in Ukrainian and in English. In English, ‘you’ is the subject, you are doing an action of ‘having’ lemons.
Ukrainian also can use this sentence structure: Ви ма́єте лимо́ни? Here, Ви is the subject, ма́єте ‘to have’ is the verb, and лимо́ни is the object.
But in «У вас є лимо́ни?», a different structure is used: ‘At your [possession], are-there lemons?’. У is a preposition that introduces a possessor, so «у вас» is translated ‘at your possession’. Here, ‘lemons’ are the subject, because they do the action of ’being’ there.
If you have further questions, don’t hesitate to ask!