It is composed of an alloy that is 90% Platinum and 10% Iridium; having a density of 21.186 g/cm3. What is the volume of the Standard Kilogram?

The alloy has a density of 21.186g/cc. So for a kilogram or 1000 grams/21.186 g/cc = 45.7 cc. So the answer is 45.7 cc of the allow to make up a kilogram which shows that the density of the allow can be used to calculate the volume of a larger mass ie the kilogram.