What are radioactive elements? What are the factors that affect radio activity?

Explanation

(i) The phenomenon of spontaneous emission of highly penetrating radiations such as `alpha,beta,gamma` rays by heavy elements having atomic number greater than 82 is called radioactivity and the substances which emit these radiations are called radioactive elements.
(ii) The radioactive phenomenon is spontaneous and is unaffected by any external agent like temperature, pressure, and magnetic fields.