Answer :
I would like to say B because it includes the colon after you will need. The commas are correct too.
Which sentence does not contain any punctuation errors?
A. For this experiment you will need; a magnet, a piece of paper, and a steel washer. B. For this experiment you will need: a magnet, a piece of paper, and a steel washer. C. For this experiment you will need a magnet, a piece of paper, and a steel washer. D. For this experiment you will need, a magnet, a piece of paper, and a steel washer.