1. 'bulk' = the majority or greater part of something, and so is seen as a single, whole entity; hence, singular verb.
2. Unless like Hawaii, (which is growing each year (from the lava flows solidifying as they hit the sea), Austrla is increasing its landmass, it is 'for Austria'.
3. I hope after asking this question I will stay in school ( I mean I hope I won't be kicked out of school . is the sentence correct?)
You're sentence as is doesn't convey that meaning. You might rephrase:
I hope after asking this question I'm not expelled (from school).
4. I hope the mistakes will/would average out
'hope' is Present tense, so the next verb must be the Present tense of the verb we use to express Future tense, 'will'
I hope the mistakes will average out.
I hoped the mistakes would average out/would have averaged out.
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