1. Increasing the pressure
In order to increase the solubility of gases in a liquid solvent, we must increase the pressure of the gas. This is the reason that the carbonation of soft drinks is carried out under pressurized conditions.
2. Supersaturated
When a solvent is "saturated", it is holding as much solute as it can at the given conditions. When additional solute is added by changing the conditions, the solvent contains more solute than normal so it is "supersaturated".
3. The concentration by weight may be calculated by dividing the weight of the solute by the weight of the solution. This is:
Weight of solute = 20 g
Weight of solution = 20 + 59 = 79 g
Wt % = (20/79) * 100 = 25.32%