Question

What is the most active element in group $17$?

Answer 1

The elements belonging to group $17$ are called halogens, these elements are termed as halogens, halo means salt and gen means formation. These halogens are salt formers with alkali and alkaline earth metals. Fluorine is the first element in group $17$ and most active or reactive element.

Complete answer:
Periodic table is the representation of chemical elements arranged in the increasing order of atomic numbers and arranged in the vertical columns and horizontal rows. The vertical columns are called groups and the horizontal rows are called periods. There are seven periods and eighteen groups in the periodic table.
The elements belonging to group $17$ are called halogens. These elements have seven electrons in their outermost orbital or shell, and try to gain one electron to attain the nearest noble or inert gas configuration.
Fluorine, chlorine, bromine, iodine and astatine belong to halogens. The Fluorine is the element with atomic number of $9$, it is the first member in halogens. It is one electron deficient to get neon configuration. It is the most electronegative element in the periodic table. Due to the less number of electrons and the short distance between the nucleus and outermost shell, it is the most active metal in the halogens.

Note:
The distance between the nucleus and outermost electrons is less in fluorine due to the nuclear attraction being more on the outermost shells. Thus, the fluorine is the most reactive or active element in the halogens due to its smaller size when compared with the halogens.