Question

How do I know the numerical subscript of an element? for example CuCl 2

Cu is copper (II), how do we know its roman number is 3

Answer 1

"The Roman numeral denotes the charge and the oxidation state of the transition metal ion. For example, iron can form two common ions, Fe2+ and Fe3+. To distinguish the difference, Fe2+ would be named iron (II) and Fe3+ would be named iron (III)."

Step-by-step explanation:

In chemistry, Roman numerals are used for a specific group of elements called transition metals. The Roman numerals indicate the charges that these metals carry in a compound.