Question

2. Why objects float or sink when placed on the surface of water?

Answer 1

If buoyant force is less than the weight of the object, then the object will sink in water. This upward force acting on the object, when an object is immersed in water is called the buoyant force. the reason behind the object float or sink depends upon its density and the density of liquid on which it is placed

Answer 2

It is due to the buoyant force
And the density decides whether the object will float or sink