Free radical
A radical is an atom or group of an (?) which possesses electric charge. There are two types of radicals: Cation and anion. Cation are positively charged while anion are negatively charged. Examples of cation are Calcium (Ca2+), Potassium (K+), Hydrogen (H+). Examples of anion are Iodide (I-), Chlorine (Cl-) and Hydroxide (OH-).