"Elements having atomic number greater than $83$ can undergo nuclear fusion". State whether the statement is true or false. If false, correct the statement.

State whether the following statements are true or false: If false, correct the statement.
During one nuclear fission on an average, $2$ to $3$ neutrons are produced.

Arrange in descending order, on the basis of their penetration power.
Alpha rays, Beta rays, Gamma rays, Cosmic rays.

Arrange the following in the chronological order of discovery.
A nuclear reactor, Radioactivity, Artificial radioactivity, Discovery of radium.

Use the analogy to fill in the blank.

Spontaneous process: Natural Radioactivity, Induced process: _____.