Here's a breakdown:
* Rydych chi - You (plural formal or singular polite)
* 'n - A contraction of "yn", meaning "are"
* anghywir - wrong
Here are some other ways to say "you are wrong" in Welsh, depending on the context:
* Rydych chi'n camgymryd - You are mistaken
* Rydych chi'n anghywir am hynny - You are wrong about that
* Nid yw hynny'n gywir - That is not right
* Mae hynny'n anghywir - That is wrong
It's important to choose the appropriate phrase based on the context and the level of formality needed.