b
(b)When particle moves away from the origin then at position \(x = {x_1}\) force is zero and at \(x > {x_1},\) force is positive (repulsive in nature) so particle moves further and does not return back to original position.
i.e. the equilibrium is not stable.
Similarly at position \(x = {x_2}\) force is zero and at \(x > {x_2},\) force is negative (attractive in nature)
So particle return back to original position i.e. the equilibrium is stable.