A uniform rod of length l is kept vertically on a horizontal smooth surface at a point O. If it is rotated slightly and released, it falls down on the horizontal surface. The lower end will remain

Since no frictional force acts on the rod , resultant acts on the rod , resultant force (mg - N ) acting on the rod us vertically downward (mg > N).

So , horizontal displacement of the centre of mass is zero , and the centre of mass starts moving vertically downward from its intial position and finally coincides with point O . Hence option - (3) is right.