Effect of pressure on solubility of salts
The answer is "(b) Decreases."  The reason is that the saturated solution occupies more volume than the starting reagents.  At higher pressures, creating this extra volume requires more $P dV$ work be done by the dissolving reagents.


  According to Le Chatelier's Principle, shouldn't equilibrium be shifted towards the side of low density when pressure is increased?


I find it easier to think in terms of volumes, not densities.  High pressure should favor low volumes.  Imagine a balloon filled with saturated solution.  If we squeeze the balloon by raising the pressure on the outside of it, the balloon will "want to" shrink.  In the example given, the balloon can shrink only by saturated solution converting back into solid salt and liquid water, so that is what would be thermodynamically favored.

Update: Based on discussion in the comments, I wanted to add a point about compressibility and thermodynamic stability.  The degree to which a system opposes a change in pressure is called the compressibility and is related to dV/dP for a given system, which you can find from the equation of state. In general, systems in thermodynamic equilibrium cannot have a positive dV/dP value. That is, the volume must shrink as pressure rises for mechanically stable thermodynamic systems.