Explanation: Frictional Force: The force exerted between surfaces to resist the relative motion between them is called frictional force. Smooth surfaces have higher frictional force as compared to rough surfaces. So, Frictional force depends upon the surface and opposes the motion. Frictional force helps us while walking. Walking on a smooth surface is difficult due to a lack of friction. Sliding is easy on smooth surfaces compared to rough ones as less friction will ensure proper movement. So, the correct statements are C, D [ height="41px" src="" width="280px"> The frictional force is given as F = μN Where μ = Coefficient of friction and N = normal reactional force on the surface [ alt="F1 J.S 18.5.20 Pallavi D 1" src="//storage.googleapis.com/tb-img/production/20/05/F1_J.S_18.5.20_Pallavi_D%201.png" style="width: 301px; height: 146px;"> The frictional force is acting against the direction of an externally applied force so as to impend the motion of the object The frictional force depends on the following factors Nature of the surface Mass of the body