Chemical Expolsives : An explosive (solid, liquid or gas) which produce high temperature and pressure released within a fraction of a second, when explosive action is initiated.

eg - Gun powder (UN No 1) - first explosive, 10 th C in China, Dynamite (by Alfred Nobel, C3H5(ONO2)2, TNT (Tri Nitro Toluene), RDX (Research Development Explosive), PETN (a plastic explosive - Pentra Erythetol Tetra Nitrate - C(CH2ONO2)4) etc.

Nuclear Explosive : Highly destructive compared to Chemical explosives. Fission (Atom bomb), Fusion (Hydrogen bomb) and Neutron bombs (destructive to living things only).

Nuclear fission (Strassman & Otto Hann in 1939) : A heavy nucleus is split into two or more lighter nuclei with tremendous release of energy. 1.3 gram of U 235 produces 1 MW of electricity.

First Atom bombs were dropped in Hiroshima (6 Aug 1945) and in Nagasakki (9 Aug 1945) in Japan by USA. The yields of the bombs were around 20 kt (of TNT).