Why is there roman numerals (ii) in copper(ii) chloride, but no (iii) in aluminum chloride?

This is because copper is a transition metals.

Transition metals don't have a definite charge, you can see this on the periodic table. However, Alkali Earth, Alkali, Metalloids, Non-metals, Halogens, Noble Gases, etc, all have a specified charge.

Although, there are exceptions: Zinc, Gold, and Cadmium.

Aluminum is a poor metal, but it has it's own charge (3+).

Therefore, Copper has roman numerals due to the fact that it's a transition metal and Aluminum is a poor metal.

Hope this helps!

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3