Whoever is one word and is pronounced like "hoo ever."
Generally, it's one word.
One is two words and the other is one. Their meaning is the same: eternal.
It is two words. Writing it as one is acceptable in the UK and is referred to as a "Britishism." But in American grammar, it is always two separate words.
Two words - "one day".
I can find no evidence to support it ever being correctly written as one word so at the present time it should be written as two. These things can change though many words that were once two were formed as one because of usage. Sometimes one of the words is even shortened as in "Alright".
Ever and Very :)
Not ever is a possibility.
I recommend class work, as two words.
It is two words.
Two words.
It's two words. :)