Concept:Equilibrium is determined by what happens to the centre of gravity when the body is slightly displaced.
Explanation:A body is in unstable equilibrium if a small displacement causes its centre of gravity to move lower and the body does not return to its original position.
Bodies I and II can roll along the horizontal table without their centres of gravity rising or falling, so they are in neutral equilibrium.
Body III has its centre of gravity G high above a small base of support, making it easy to topple; therefore, it is in unstable equilibrium.
Body IV is in stable equilibrium because its centre of gravity is low and, when displaced, it tends to return to its original position.
Thus, only body III is in unstable equilibrium.
Answer:III only, which is Option B.
