Karim, and Hasan are

Karim, and Hasan are--------
Karim and Hasan are--------
Which one is correct and why not the other one?

Assuming this is the beginning of a sentence, and not a fragment from the middle of a sentence, the second is the correct option.
Commas are used to separate items (including people) in a list, but are not used before the last item. An ‘and’ is used instead.

John, Mary, Karim and Hasan…

John, Mary, Karim, and Hasan…
False?

Not standard punctuation unless there is a particular purpose for the extra pause/separation.

I think, Farmer1’s version is American English. Am I right?

No.

You are thinking of the “serial comma”, a comma placed before “and” at the end of a list of items. For example, “The prizes were awarded to John, Mary, Karim, and Hasan.” This is usually said to be more commonly, though not exclusively, used in AmE.

I can’t seem to find any explicit discussion of whether (in AmE or elsewhere) the serial comma can legitimately be used other than at the end of a sentence. The explanations I have found seem to just ignore that case, and only give end-of-sentence examples. However, patterns like “John, Mary, Karim, and Hasan went to school” look definitely wrong to me, as Beeesneees has said.

Hi Farmer,
This sort of comma is also called an Oxford comma (which would lead one to believe it’s more British) as well as a Harvard comma (which, of course, suggests American). I’m American, and I never use a serial comma in a simple, straightforward list. I know plenty of Americans who also do not use it. Basically, the only time I use a serial comma is when the components of the list are fairly complex, and the use of this comma will help avoid confusion. On the the other hand, I also know some people who use it with every list, no matter what sort of list it is.

You might find this link helpful:
Serial comma
(The serial comma is discussed in #1.)

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[size=75]“Cast iron rules will not answer what is one man’s colon is another man’s comma.” ~ Mark Twain[/size]

Are mid-sentence uses like “John, Mary, Karim, and Hasan went to school” ever acceptable in AmE, as far as you know?