"Which size…" sounds slightly more likely if we're standing in front of a wall of the same product in every size, and "what size…" slightly more likely if the clerk is going to go back to the storeroom for it; but either form is idiomatic enough in any context I can think of.
Yes, it changes depending on gender and number.
Masculine: ну́жен - «Мне ну́жен нож», «Ма́тери ну́жен некоторый хле́б.»
Neuter: ну́жно - «Ди́ма сказа́л, что ему́ ну́жно пи́во; он не хо́чет пиво.»
Feminine: нужна́ - «Ему нужна́ крова́ть, чтобы спать, но у него кровати нету.»
Plural: нужны - «Мне не нужны некакие лека́рства, мне то́лько ну́жен лека́рь.»
Hope what helped!
EDIT: Corrected according to @keinemeinung’s recommendation below. Спасибо!
Thanks, but what if I want to say ‘Mother needs some bread’ instead of just simply ’Mother needs bread’? ’I need some medicine’, instead of simply ’I need medicine’. Would you use надо instead.
Спасибо за исправление!
EDIT: Oh, now I understand. I used the genitive because the sentences are negative (не, не...).
Also, you would use the adjective некоторый or несколько to convey a concept of ’some’ in these cases, right?
With нужны it can carry the sense of "some" without kicking the noun into partitive genitive (took five tries to type that lol). But yeah you make a good point that adjectives can also emphasize that meaning if the noun is a quantifiable/countable thing.
edit: Like you can't say некоторый хлеб as that would convey the meaning of "some (types of) bread" as opposed to "an amount of bread".
Is «Маме нужен несколько хлеба» OK or do you have to use надо?
You have to use "нужно" 'cause here it has to agreе with "несколько" not "хлеба".
Also "несколько" is for the countable nouns. "Хлеб" is a mass noun, so you have to use "немного".
So the correct sentence would be "Маме нужно немного хлеба".
In theory one can say "несколько хлебов" meaning several types of bread, but that's not very common expression.
I was actually hoping to learn that it's virtually the same. Russian is hard enough, so I am desperately looking to find as many things that are the same or similar to Croatian that I can :D
So far I got the impression that word order, while technically nearly irrelevant in both languages, seems to matter a little more in Russian. I cannot think of any examples right now, but there were some things that apparently shouldn't (not couldn't!) be said in certain ways, whereas in Croatian it was pretty much whatever :)
Would "какой вам нужен размер?" focus on what size you need vs. other sizes that wouldn't fit you, while "какой размер вам нужен?" focus on what size YOU need vs. what other people might need? E.g., if there are four people waiting in line for bowling shoes, and you are the fourth one, and the attendant says "OK, you're next, now for you as opposed to the last three people: what size do YOU need?"
"OK, you're next, now for you as opposed to the last three people: what size do YOU need?"
That would be better expressed with "какой размер нужен вам?"
"Какой размер вам нужен" focuses more on "need"/"require". So it can be said with a sigh and an implied "what else do you need from me?". But with a neutral intonation it wouldn't sound too different from "какой вам нужен размер?". It's just that the latter is unlikely to be used as an expression of exasperation, whereas the former might be.
You could also get away with "Kakoj razmer vam nuzhen?", or with certain intonation "Vam nuzhen kakoj razmer?" (this sounds better spoken as opposed to written in my opinion). I'd have to say that in this case it's "Kakoj vam nuzhen razmer?" so that the adjective "nuzhen" and the noun it's modifying (razmer) are collocated in the sentence in a logical order.