Final answer:
The force that holds two atoms together is called a chemical bond, which is an electrical attraction that forms a molecule or compound, with ionic and covalent being types of these bonds.
Step-by-step explanation:
The force responsible for holding two atoms together is known as a chemical bond. A chemical bond is an electrical attraction that can be either weak or strong, and it holds atoms close to one another forming a more stable arrangement known as a molecule. When a molecule consists of two or more different elements, it's called a chemical compound. The nature of these bonds can be ionic or covalent. In ionic bonds, electrons are transferred, creating ions that stick together because of electrostatic attraction. In covalent bonds, electrons are shared between atoms, creating a strong force of attraction between the positive nuclei and the shared pairs of electrons.
Therefore, the correct answer to the question is b. chemical bond.