An orange sits on a table in equilibrium. What forces are acting on it? What is the reaction force to each of the forces acting on it? What are the action and reaction pair?
Force of gravity and normal reaction by table are not action reaction pair. Due to gravity, the object (here orange) exerts a force equal to its weight W=mg on the table and then the table exerts equal and opposite force which is normal reaction in this case. If the surface makes an angle, say A, with horizontal, then the normal reaction will be perpendicular to surface but will not be equal to mg. Instead, normal reaction force in this case is N=mg cos(A)