Oxygen, sulphur, selenium, tellurium, polonium and livermorium constitute Group 16 of the periodic table. This is sometimes known as group of chalcogens. The name is derived from the Greek word for brass and points to the association of sulphur and its congeners with copper. Most copper minerals contain either oxygen or sulphur and frequently the other members of the group.

The elements of Group16 have six electrons in the outermost shell and have ns²np⁴ general electronic configuration.

Due to increase in the number of shells, atomic and ionic radii increase from top to bottom in the group. The size of oxygen atom is, however, exceptionally small.

Which of the following is radioactive in nature?

Polonium

The correct answer is option 4. Polonium.

The element that is radioactive in nature from the options provided is Polonium.

Polonium (Po) is a radioactive element. It is a highly unstable element and exhibits radioactive decay, emitting alpha particles. Polonium has several isotopes, but the most common and well-known isotope is polonium-210 \((^{210}Po)\), which is radioactive. Due to its radioactive nature, polonium is hazardous to health and poses a significant radiation risk if ingested or inhaled. Oxygen (O), sulfur (S), and tellurium (Te) are stable non-radioactive elements and do not naturally exhibit radioactive properties under normal conditions.