The correct option is C Box (iii)
When all the forces acting on a body are equal in magnitude but opposite in direction such that they cancel each other's effect, they are said to be balanced else they are unbalanced.
Case (i): The two forces are acting in opposite directions with unequal magnitudes. Thus, the forces are unbalanced.
Case (ii): The two forces are acting in same direction with equal magnitudes thus they do not cancel each other. So, they are unbalanced.
Case (iii)- Though both the forces are acting on the same side of the box, their directions are opposite; and their magnitudes are equal. Thus, the forces cancel out each other and hence are balanced.