Final answer:
The type of force exerted when pushing someone is a contact force, specifically frictional force. The force responsible for holding an atom together is an electric force.
Step-by-step explanation:
When you put your hands on someone and push, you are exerting a contact force. The correct type of force in the context of this action is B) Frictional force. Contact forces occur due to direct physical contact between objects, and include forces such as tension, friction, normal force, spring force, and even the force you exert when pushing against someone. In contrast, forces such as gravitational, electrostatic, magnetic, and centripetal forces are field forces which act without the necessity of physical contact.
For the force responsible for holding an atom together, it is B) electric. This force arises because of the electric charges of the protons and electrons within the atom, making it an electromagnetic force. This is not a gravitational, frictional, or magnetic force, which act on different principles and at different scales.