"Wyt ti'n iawn?"
Translation:Are you all right?
Formally that would be 'dych chi'n gywir' = you are correct
Informally people use 'iawn' (dych) chi'n iawn or (rwyt) ti'n iawn - very often the verb is omitted.
The same with the question is that correct? = 'Ydy hynny'r gywir?' would be more formal
'Ydy hynny'n iawn?' - less formal.