Indium (In). Diagram of the nuclear composition and electron configuration of an atom of indium-115 (atomic number: 49), the most common isotope of this element. The nucleus consists of 49 protons (red) and 66 neutrons (yellow). 49 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). The stability of an element's outer electrons determines its chemical and physical properties. Indium is a post-transition metal in group 13, period 5, and the p-block of the periodic table. It has a melting point of 157 degrees Celsius. Similar to gallium and thallium, it is used in liquid crystal displays and touchscreens.