Ans: PETN is majorly used as an explosive by different countries and several terrorist organizations. It can be directly used as an explosive or as a mixture with other explosives like TNT. The mixture of PETN with TNT is called Pentolite. It is also mixed with RDX in an appropriate solvent to form the Semtex mixture. PETN is more stable than nitrocellulose and nitroglycerin.The first use of PETN dates back to world war I. The German military forces used it. PETN was also used in World War II in projectile artillery and shaped-charge warheads. Several terrorist organizations use PETN directly or as a mixture, like the Semtex mixture. They loved this compound because of its explosive nature, ability to be molded and fixed into different shapes and packages, and difficulty to detect by conventional X-ray-based methods. There are numerous reported terrorist attacks and attempts that used PETN.