Statement (A) : The mass number of Oxygen is 16. 

Statement (B) : The mass number of Calcium is 40. 

Statement (C) : The mass number of Copper is 63.5

For an atom of element mass number A should be equal to sum of the no. of protons and neutrons present in the nucleus. Hence, A=p+n;

Hence mass number of an element should be positive integer

For oxygen(Z= 8), mass no. A = 16

For calcium(Z =20) mass no. A = 40

For copper (Z 29 = ), mass no. A= 63.5