An over saturated solution is best described by option A: it contains more solute than it can exist in equilibrium at a given temperature and pressure.
To elaborate, a saturated solution is one where the maximum amount of solute has been dissolved in a solvent at a specific temperature and pressure. When an over saturated solution is formed, it means that additional solute has been added beyond this saturation point, resulting in a state where the solution can no longer hold all of the solute in dissolved form. This often occurs if the solution is heated or manipulated in other ways, allowing for more solute to be dissolved temporarily. However, once the conditions stabilize, the excess solute will likely precipitate out, returning the solution to a saturated state.
Option B is incorrect because, while more solute might initially dissolve, eventually, it will reach a point where no more can dissolve without forming crystals. Option C is also not a relevant description of what defines an over saturated solution, as it misrepresents the relationship between solute and solvent in such a scenario.