In which case is a comma typically used incorrectly?

A comma is typically used incorrectly between two independent clauses without a conjunction because this can create a comma splice. A comma splice occurs when two complete sentences (independent clauses) are wrongly joined by just a comma, lacking a coordinating conjunction (like 'and,' 'but,' or 'or'). For instance, in the sentence "I went to the store, I bought some milk," the comma does not effectively connect the two independent clauses; thus, it creates confusion and disrupts the flow of the sentence.

In contrast, a comma before 'and' in a list is standard practice when listing three or more items, ensuring clarity. Similarly, placing a comma before a conjunction in a compound sentence is correct, as it signals the break between two independent clauses. Lastly, it is also correct to use a comma after introductory phrases to separate them from the main clause, improving readability. Therefore, the use of a comma between two independent clauses without a conjunction stands out as a misuse, making the option highlighting this incorrect usage valid.