Answer:
New force, 
Explanation:
The electrostatic force between two spheres is given by :

According to given condition, each of the spheres has lost half its initial charge, new force is given by :



So, the new force becomes (1/4)th of the initial force. Hence, the correct option is (d).
Windmills run on the principle of mechanical energy and work. Moving air (wind) possesses some amount of energy in the form of kinetic energy (due to motion). This energy gives the air the ability to do work on the blades of the fan.
It's a chemical chemical change
The answer is C, because they moved from a stand still to down the hill