Questions & Answers about Бабушка налила мне супу.
Why is the ending -у used in супу instead of the normal genitive -а?
Because суп is a mass noun being used to mean 'some soup'. This is called the partitive genitive (or second genitive). Certain masculine uncountable nouns take an -у or -ю ending when you are talking about a portion or quantity of them. Saying супа is also grammatically correct, but супу sounds very natural and traditional for a portion of food.
Could I use the accusative case суп here instead?
Yes, but it changes the nuance. Saying Бабушка налила мне суп (accusative) sounds like she poured 'the soup' (perhaps a specific, single serving that was prepared). Using the partitive genitive супу makes it crystal clear that she poured 'some soup' out of a larger pot.
What does the prefix на- add to the verb налила?
The verb налила is perfective, focusing on the completed result of pouring. The prefix на- often carries the specific meaning of filling a container or accumulating a certain quantity of something. If you used the base imperfective verb лила, it would just describe the physical action of spilling or pouring a liquid, without the sense of serving a portion.
Why does мне come before супу?