This is the 9799th most frequent Russian word.
яблоко
Apple.
In this sentence, 'яблоко' is used in the nominative case as the subject of the sentence, depicting a single apple.
Яблоко лежит на столе.
The apple is lying on the table.
Here, 'яблок' is used in the genitive plural case to describe the quantity of apples purchased.
Я купил килограмм яблок.
I bought a kilogram of apples.
In this sentence, 'яблоко' is used in the accusative case as the direct object receiving the action of the verb 'дала' (gave).