In the listed translations both are shown so it's unclear what the difference is with the usage.
Wei is informal, ni hao is more formal. If anything hello is ni hao and hi is wei
It's appearing in a placement test, where it's not necessarily clear that this is answering the phone - so I went ni hao then wei, as that felt more accurate. Perhaps shouldn't be in the placement test?
I suppose it delends on how you speak English.
喂 is what you say when you answer the phone. 你好 is a greeting.
I personally say "Hello?" when I answer the phone. I say "Hi" or "Hey" as a greeting. I believe this is consistant with the majority of English speakers where I am from (mid-Atlantic US). However, it wouldn't be grammatically wrong to interchange "Hello", "Hi", and "Hey" (although you would be changing levels of formality).
Apologies, I misread the character you were asking about. I have never encountered the character 嗨 before. I suspect it is simply a transliteration of the English "hi" but that is just a guess.
Might be clearer if the question read "hello? Hello!", since 你好 is translated as hello elsewhere.
we don't say hello hi in English we say hello how are you, which is a better translation anyway
Think about answering a phone. You realize who the caller is between "Hello?" and "Hi!"
'Hello' and 'Hi' both are greeting, a sound made to attract attention and does not have bearing of how are you (你好).
The literal translation of 你好嗎 may be "how are you" but that doesn't mean that it is not used as a general greeting. Learning a language doens't just include being able to perform literal translation, it also includes understanding which phrases to use in which situation, and in this case 你好 is a generic greeting like "hello".
喂你好: absolute standard way to answer the phone in China. Which reminds me of how French people sometimes answer the phone with: Oui, bonjour! Oui does sound a bit like 喂 i think ;) Though the way they say 喂 in china certainly deserves a question mark to get the tone of voice right..