When electrons are gained, the charge of the atom decreases.
When you are given an atom with a charge, the oxidation of that atom is the charge. So by going from a Cr^3+ (Oxidation Number = 3) to a Cr^2+ (Oxidation Number = 2), the Oxidation Number thus decreases.
Density of a solution is mass of solution per unit volume Density = mass/volume mass of solution is 46.08 g volume of solution is 58.9 mL since mass and volume is known, density can be calculated density = 46.08 g / 58.9 mL = 0.78 g/mL
