What change occurs to anhydrous copper(II) sulfate when it is mixed with water?

When anhydrous copper(II) sulfate is mixed with water, it undergoes a physical change called hydration. This process results in the formation of hydrated copper(II) sulfate, which is typically known as copper(II) sulfate pentahydrate. The key visual change that accompanies this process is the transformation from a white or greyish-white solid to a vibrant blue solution.

The blue color is indicative of the presence of water molecules coordinated to the copper(II) ions, which alters the electronic structure of the compound. The interaction between the water molecules and the copper ions causes a change in the way light is absorbed and reflected, leading to the distinct blue coloration.

This characteristic blue color serves as an important indicator in many chemical applications, demonstrating the process of hydration effectively. The other color options provided do not accurately represent the change that occurs during the hydration of anhydrous copper(II) sulfate.