Q1: What is radioactivity? A: The phenomenon of spontaneous emission of alpha particle or beta particle and gamma rays from an unstable nucleus is called radioactivity. Q2: When does a nucleus become unstable ? A: When the number of neutrons become much more than that of protons. Q3: Which part of the atom takes part in radioactivity ? A: Nucleus Q4: What happens to the radioactive behaviour of a radioactive sample if it is chemically oxidized ? A: The radioactive behaviour does not change. As oxidation is the chemical change, it does not affect the nuclear activity. Q5: How does the atomic number and mass number change if a radioactive nucleus releases one alpha particle ? A: Atomic number decreases by 2 and mass number decreases by 4 Q6: How does the atomic number and mass number change if a radioactive nucleus releases one beta particle? A: Atomic number increases by 1 and mass number does not change.