<i>My friends are Solen, Karen, Mico, and Jon. </i>(with comma before "and")<br/><br/><i>My friends are Solen, Karen, Mico and Jon. </i>(no comma before "and")<br/><br/>Which of the sentence above is correct with regard to using comma (,)<br/><br/>Is comma (,) always necessary before the word "and"? Is it more appropriate in formal writing?