An ion is an atom that has lost or gained an electron so the relation ship you would see would be a negative or a positive one depending on if it gained or lost an electron.<span />
Because the speed of light is determined by the medium that is it in. If light is in a vacuum it goes 300 million meters per second but it is slower in air, and even slower in water because water is more dense than the previous two.
Solubility in water Anhydrous: 74.5 g/100 mL (20 °C) Hexahydrate: 49.4 g/100 mL (−25 °C) 59.5 g/100 mL (0 °C) 65 g/100 mL (10 °C) 81.1 g/100 mL (25 °C) 102.2 g/100 mL (30.2 °C) α-Tetrahydrate: 90.8 g/100 mL (20 °C) 114.4 g/100 mL (40 °C) Dihydrate: 134.5 g/100 mL (60 °C) 152.4 g/100 mL (100 °C)