The given plot shows the variation of U, the potential energy of interaction between two particles, with the distance separating them, r : 

1. C is a point of stable equilibrium 
2. The force of interaction between the two particles is attractive between points C and D and repulsive between points D and E on the curve. 
3. B and D are equilibrium points
4. The force of interaction between the particles is repulsive between points E and F on the curve. y-interaction-between-particles-distance-separating

1 and 2

1. At point 'C', the potential energy is minimum, hence it is a point of stable equilibrium.
2. Also, from E to F, the slope is negative i.e., \(\frac{dU}{dx} < 0\) Hence, the force of interaction between the particles is repulsive between points E and F.