Question

Which sentence is punctuated correctly?



I used the green pen not the red one for my homework.


I used the green pen, not the red one, for my homework.


I used the green pen, not the red one for my homework.

Answer 1

"I used the green pen, not the red one, for my homework."

The phrase "not the red one" is a parenthetical/contrasting interrupter and should be set off on both sides with commas.