Question

what is meant by buoyant?why does an object float or sink when placed on the surface of a liquid

Answer 1

If a body is partially or wholly immersed in a fluid. It experiances an upward force due to the fluid surrounding. This phenomenon of force exerted by fluid on the body is called buoyant force.

Answer 2

You can say it's a type of force or something that is able or tending to keep afloat or rise
to the top of a liquid or gas.

The
name of this upward force exerted on objects
submerged in fluids is called the buoyant force . It has to do with
differences in pressure between the bottom of
the submerged object and the top.
Because pressure (P = ρgh ) increases
as you go deeper in a fluid, the force from
pressure exerted downward on the top of the
can of beans will be less than the force from
pressure exerted upward on the bottom of the
can.
Essentially it's that simple. The reason there's a
buoyant force is because of the rather
unavoidable fact that the bottom (i.e. more
submerged part) of an object is always deeper in
a fluid than the top of the object. This means
the upward force from water has to be greater
than the downward force from water.