The atomic bomb is a nuclear weapon that uses the phenomenon of nuclear fission to cause massive explosions that causes immense physical damage over a large area.
When the large nucleus of an atom breaks down into smaller-sized nuclei and forms new atoms (of smaller size and atomic number), a huge amount of energy is released. This process is known as nuclear fission.
The first atomic bomb was made by a team from America, which was led by theoretical physicist J. Robert Oppenheimer.