Which of the following statements regarding copper salts is not true?
a. Copper (I) disproportionates to copper and copper (II) ion in aqueous solution
b. Copper (I) can be stabilised by the formation of insoluble complex compounds such as CuCl2− and Cu(CN)2−
c. Copper (II) oxide is red powder
d. The water of crystallization of copper sulphate is five