Explanation

(a) From law of floatation, we know that a body will float in a liquid, when its weight W is equal to the weight $w$ of the liquid displaced by the immersed part of the body will be in equilibrium. A body will be in equilibrium only, if the resultant of all the forces and couples acting on the body is zero. If W and w act along different lines, they will from a couple which will tend to rotate the body. Thus, a floating body can be equilibrium, if no couple acts on it. It will be so, if the line of action of W and w is along the same vertical straight line.
Here, in both the situations, as the mass of floating block remains same, hence according to principle of floatation mass of volume of water displaced also remains same. Hence, water level will remain same in both the cases.