hey m still confused...................
Ok no prob we will take it step by step:
1) what does equillibrium mean?
it means that they are not moving right?
This means there is equal forces on each side acting downwards
2)since pressure= force/area so equal pressure because equal forces acting on equal areas (vessel) and pressure is equal to density*gravity*height
3) however height of P is doubled than of Q so new pressure will be doubled of Q but
we must get EQUAL pressures and also gravity is not changed so density must be halved at P to get same pressure
so now we have half density of P since double height
Note:try with values if u still don't get it and see what happens to density
