Solution:concept - When an element shares electrons with other atoms of the same or different elements to obtain a stable electron configuration, it is called covalency.
The number of electrons in an atom's outer shell is known as its valence. If the number of electrons in the outermost shell of an atom is less than the total number of electrons in its fully filled configuration, then the atom tends to reach the nearest noble gas configuration. It can do so either by sharing its electrons with other atoms or by losing and gaining electrons.
When an atom reaches stable configurations by losing or gaining an electron (or electrons), the number of electrons lost or gained is called its electrovalency. E.g. in , Na has one electron as the outermost shell ( ). It loses this one electron to reach the stable noble gas configuration of Na. This lost electron is gained by the Chlorine atom in .
When an atom shares its electrons with other atoms (or an atom), the number of electrons shared by the atom is called its covalency. Compounds formed by sharing electrons between atoms are called covalent compounds.
Hence, the correct option is (2).