The correct option is B Both A and R are correct and R is not the correct explanation of A
Co-factors are non-protein constituents bound to an enzyme to make it catalytically active. They are can be prosthetic groups, co-enzymes or metal ions.
When the co-factors are organic compounds, they are considered to be "prosthetic groups".
Coenzymes are also organic compounds that bind to enzymes, but they bind very loosely.
Hence A and R are correct but R does not explain R.