GALLIUM PHOSPIDE: It has band gap of 2.3ev. it can be used for light emitting diodes which can emit  green or red light. The red light is obtained with zinc or cadmium oxide doping.                                                               

SELENIUM: It is found in crystalline and non-crystalline form. It is used as rectifier material for photo voltaic cells and for xerographic printing. Selenium films are used as photo electric light meters. Its melting point is 220⁰C.

LEAD: it is soft heavy and bluish gray metal. It is highly resistant to many chemical actions but can corrode by nitric acid, lime and rotten organic substances. Lead and its compounds are toxic. It is mechanically weak it cannot withstand vibrations at high temperatures. It alloys easily with Tin and zinc and forms many commercial alloys, including solders and bearing metals.