the correct choice is
The buoyant force is greater on the rock in water
Explanation :
The buoyant force acting on a rock completely submerged in a fluid is given as
F = ρ V g
here F = force of buoyancy
V = Volume of fluid displaced by the rock (in case of object completely inside the fluid, the volume of fluid displaced is same as the volume of object)
g = acceleration due to gravity.
from the formula , the force of buoyancy "F" in upward direction is directly proportional to the density of fluid displaced. that is , greater the density of fluid , greater will be the force of buoyancy.
we know that density of water > density of air.
hence the rock experience greater force of buoyancy inside water as compared to when in air.
greater force of buoyancy inside water makes it easier to lift the rock in water.