The correct answer is C. Halogen group.
The halogens are a group of elements in the periodic table that are highly reactive and form salts with metals. They are all non-metals and exist as diatomic molecules in the gas phase. The halogens are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Fluorine is the most reactive element in the periodic table. It is a pale yellow gas that is extremely poisonous. Chlorine is a greenish-yellow gas that is also poisonous. Bromine is a reddish-brown liquid that is also poisonous. Iodine is a purple solid that is less poisonous than the other halogens. Astatine is a radioactive element that is so rare that its properties are not well known.
The halogens are all highly reactive because they have seven valence electrons. This means that they need to gain one electron to form a stable octet. They do this by reacting with metals to form salts. For example, chlorine reacts with sodium to form sodium chloride (NaCl), which is common table salt.
The halogens are also used in a variety of other applications, such as in the production of plastics, pharmaceuticals, and pesticides.