What is the VX chemical weapon which was used to kill Kim Jong Nam, the half-brother of the North Korean leader Kim Jong-il?
VX is the "most toxic of all known chemical warfare agents", and is about 100 times as powerful as sarin. One drop can reportedly kill a person within minutes. It is banned by the 1993 Chemical Weapons Convention, which means states should not hold any stockpiles of it. Its chemical name is S-2 Diisoprophylaminoethyl methylphosphonothiolate.