No, CO3N2, if such a compound exists is a covalent compound and is composed of 3 elements. A binary compound is composed of exactly two elements. However, you are you probably mean Co3N2, which is a...
a cation and an anion
No, CBr4 is a covalent compound.
The chemical formula KCl is for potassium chloride.
No, it consists of 3 elements (to be binary is can only have 2) and is covalent.