What is electronegativity?

Hint: We have to know that the electronegativity example can be explained by looking \[HCl\] molecule in which \[C{l^ - }\] is an electronegative atom whereas \[{H^ + }\] is electropositive and the bond so formed is covalent. Group $17$ belongs to the halogen family.

Complete answer:
We have to remember that electronegativity is the property in which an atom can attract shared pairs of electrons towards itself. An atom’s electronegativity is affected by both atomic number and valence electrons inside the nucleus. Electronegativity increases when on moving from left to right and decreases on going down the period. In halogens, i.e. group $17$, the position of elements in a periodic table is:
$F$
$Cl$
$Br$
$I$
\[F\] is most electronegative atom in group $17$ \[Cl\] being more electronegative than \[Br\] and less electronegative than \[F\].When we moves down in a group, the atomic number increases as the atomic shell is increased, hence the effective nuclear charge increases due to which electronegativity decreases. Metals usually have lower electronegativity as they are electropositive in nature.
For Example: \[Na\], \[Sr\]
Also due to the electronegativity concept we can refer to the covalent bonding in certain molecules. Since covalent bond is formed by two molecules having different electronegativity in which more electronegative atom forms anion and least electronegative atom forms cation.

Note:
We have to know that the elements that have low ionization energy will have low electronegativity and electronegativity is inversely proportional to atomic radius. Metals usually have lower electronegativity as they are electropositive in nature. Alkali metals and alkaline earth metals are electropositive in nature which is just an opposite of electronegative. Halogens are said to be electronegative i.e. group $17$; in which \[F\] is the most electronegative element.