Final answer:
Energy can be supplied to release an electron using electrical energy from a discharge tube or batteries for electrolysis, and high-energy photons like in X-ray production.
Step-by-step explanation:
To release an electron from an atom, energy needs to be supplied in various ways. One of the methods is by applying electrical energy, such as passing an electric current through a gas at low pressure in a discharge tube, which leads to a distinctive glow based on the gas present.
A second way is by using a power source like a battery to induce a chemical reaction, for instance, electrolysis of water into hydrogen and oxygen gases. The addition of energy can also be through high-energy photons in X-ray production, where an electron is accelerated and strikes a metal target to produce X-rays.