Final answer:
The comma is incorrectly placed in the sentence after the word 'four' because 'four students' is a connected noun phrase, and there's no need to separate them with a comma.
Step-by-step explanation:
A comma is a commonly used punctuation mark that is used to separate two words, phrases or clauses in a sentence. It can also be used in a list to mention different items or articles. The comma is placed incorrectly in the sentence "Six students sit at my table group but four, students sit in that table group." because it should not be inserted between the word 'four' and 'students', which are directly connected as a noun phrase.
In this case, the comma is not needed at all because the conjunction 'but' is connecting two independent clauses, and 'four students' is not extra information that can be removed without altering the essential meaning of the sentence. We can also compare this with common comma rules such as placing commas around non-essential information or using commas in a series, which do not apply in this context.