The correct answer is A) Gravitational force is considered to be the weakest of the four fundamental forces.

It is responsible for the attraction between objects with mass, such as planets and stars, and is responsible for the force of gravity experienced by all physical objects on the surface of the earth.

The gravitational force between two objects is inversely proportional to the square of the distance between them and directly proportional to the product of their masses.

Additional Information option wise 

1. B) Electromagnetic force is the force that holds atoms and molecules together and is responsible for the interactions between electrically charged particles. It is much stronger than the gravitational force and is responsible for phenomena such as magnetism and electricity.
2. C) Nuclear force is the force that holds the protons and neutrons in the nucleus of an atom together. It is much stronger than the electromagnetic force and is responsible for phenomena such as radioactive decay and nuclear fusion.
3. D) Electrostatic force is the force of attraction or repulsion between two electrically charged objects. It is a type of electromagnetic force and is responsible for phenomena such as static electricity.

So, therefore the correct answer is A) Gravitational force