B, the chemical formula of potassium nitrate is KNO3, so B is correct;
C, the unit of molar mass is not g, and the molar mass of potassium nitrate is 10 1g/mol, so c is wrong;
Potassium ions and nitrate ions in D and KNO3 _ 3 ionized solutions are not easy to precipitate with other ions, so it is difficult to have a metathesis reaction, so D is correct.
So choose C.