Answer:
Electrons
Explanation:
In an atom there would be three subatomic particles: Neutrons, electrons, protons. The smallest and lightest in terms of mass is electrons. This is because the nucleus is comprised of the protons and the neutrons, these have a greater mass than electrons as electrons has very little mass that can considered to be 0.
Answer: When the reaction reaches equilibrium, the cell potential will be 0.00 V
Explanation:
Equilibrium state is the state when reactants and products are present but the concentrations does not change with time.
The equilibrium is dynamic in nature and the reactions are continuous in nature. Rate of forward reaction is equal to the rate of backward reaction.
The standard emf of a cell is related to Gibbs free energy by following relation:

The Gibbs free energy is related to equilibrium constant by following relation:

For equilibrium 
Thus 

Thus When the reaction reaches equilibrium, the cell potential will be 0.00 V
The gravitational force between the objects depends on the mass of the objects and the distance between them.