Where to put "yet" (word order)

I'd go with the first, but I'd actually prefer getting rid of the word "yet" altogether. It accomplishes nothing.

Insofar as I understand it, they really could be used either way, but I've seen usage patterns that make some sense to me.

In your first example, where it is an ongoing process, I would tend toward "not yet known." And in your second, where as of right now Mike has either arrived or he hasn't, I suggest "arrived yet".

Yet is an adverb, and like other adverbs, it's flexible and can go in a lot of places. Listen to the sentence and see which one sounds better. To my ear, "Mike has not arrived yet" sounds better.

The "guideline" about split infinitive still applies. You probably don't want to write "He has to yet go where no man have gone before."

And I'd say, "...has yet to arrive." But then, my voice tends to be somewhat formal.

Either option is acceptable. Use the one that fits the voice of the character and overall MS.

Correct is "not yet known." "not known yet" is colloquial, but acceptable, if informal.

Two points. There is no reason to assume it will ever be known, so the 'yet' cannot be justified. Secondly, isn't any function exact? You either know about it or you don't.

In this case, I think it is your arbitrary decision. As an adverb it can go after 'not' or at the end.

Incidentally, the Google search probably includes a lot of cases where 'yet' is used as a concunction ( like 'but'). The results are also likely to be biased because the search doesn't specifically relate to complete sentences.

Yet another question that has no answer!