Correct Option
Gravity is the weakest of the four fundamental forces of nature. Its influence becomes significant only when dealing with objects of very large mass, such as planets and stars. At the subatomic scale, its strength is negligibly small compared to the electromagnetic, weak nuclear, and strong nuclear forces. Therefore, the statement that gravity is the strongest of the four is incorrect.
Incorrect Options
Electromagnetism acts only on particles with an electric charge: The electromagnetic force acts exclusively on particles that possess an electric charge, such as protons and electrons. Neutral particles, like neutrons, do not experience this force directly. This statement is factually correct.
Weak nuclear force causes radioactivity: The weak nuclear force is responsible for certain types of radioactive decay, notably beta decay, which involves the transformation of a neutron into a proton (or vice versa) with the emission of an electron or positron and a neutrino. It plays a crucial role in nuclear reactions within stars. This statement is factually correct.
Strong nuclear force holds protons and neutrons inside the nucleus of an atom: The strong nuclear force is the most powerful of the four fundamental forces. Its primary function is to bind protons and neutrons together within the atomic nucleus, overcoming the strong electrostatic repulsion between positively charged protons. This force has a very short range, acting only over subatomic distances. This statement is factually correct.