The correct option is
D At
The explanation for the correct answer:-
Option(D)
- Radioactive elements are elements that transmute into other elements by decaying various types of fundamental particles.
- Radioactive elements are extremely hazardous as radioactivity interferes with biological life and causes severe harm to them.
- Astatine is a radioactive element that belongs to the halogen group.
The explanation for the Incorrect answer:
Option (A)
- Cl (Chlorine) belongs to the halogen family and is toxic to human health but is not radioactive.
- Therefore, this option is incorrect.
Option(B)
- Br (Bromine) is a brown-colored liquid and this element belongs to the halogen family, it is toxic to human health but is not radioactive.
- Therefore, this option is incorrect.
Option (C)
- Po (Polonium) is a radioactive element but it belongs to Group-16, the chalcogens, and the oxygen family.
- Therefore, this option is incorrect.
Therefore, radioactive halogen is Astatine.
Hence, the correct option is (D).