Which of the following elements is non-radioactive?
(1) Uranium
(2) Thorium
(3) Plutonium
(4) Zirconium
Answer: (4) Zirconium is non-radioactive. It is a chemical element with the symbol Zr, atomic number 40, and atomic mass of 91.224. The name of zirconium is taken from the mineral zircon, the most important source of zirconium. It is a lustrous, grey-white, strong transition metal that resembles titanium. Zirconium is mainly used as a refractory and opacifier, although minor amounts are used as an alloying agent for its strong resistance to corrosion.
