Define buoyant force.An object of volume 5 cm3 is immersed first in water and then in salt solution. In which case will it experience a greater buoyant force ? What will be the effect on the buoyant force, if the volume of the object is increased to 8 cm3

Whenever a body is immersed in a liquid, it experiences an upward thrust which is equal to the weight of the liquid. This upward is called the buoyant force.
The object of volume 5 cm^3 immersed in the salt solution will experience a greater upward thrust because upthrust (= V x d x g) because of larger density of the salt solution.
When the volume of the object is increased, the upward thrust will also increase because of the increase in the volume of the liquid displaced.