What do you mean by buoyant force?
It is defined as the upward force exerted by a fluid on a body immersed in it.
What is specific gravity of a substance?
Specific gravity of a substance is defined as the ratio of density of a substance to the density of water (for solids and liquids) and hydrogen (for gases).
What is a fluid?
A substance which has no shape of its own but takes the shape of the vessel containing it, is called a fluid.