Concept:In covalent bonding, some valence electrons remain unshared.
These unshared pairs are known as lone pairs.
Explanation:Outermost shell electrons are called valence electrons.
They can participate in bonding as shared pairs or bonding pairs.
However, not all valence electrons are used for bond formation.
A pair of valence electrons that is not shared with another atom is called a lone pair.
It is also known as a non-bonding pair or unshared pair.
For example, in a water molecule, oxygen has two lone pairs of electrons.
These lone pairs occupy the outermost shell but do not take part in bonding.
Hence, the pair of outermost shell electrons not used in bonding is the lone pair.
Answer:A. lone pairs