Ammonia NH₃ contains only one unshared pair of valence electrons. Therefore, option (A) is correct.
Valence electrons can be defined as the electrons in the outermost shell of an atom while the electrons occupying the inner shell are called core electrons. Valence electrons can be filled in different shells and these electrons interact with other atoms and cause the formation of chemical bonds.
In ammonia, the central atom is nitrogen and nitrogen has five valence electrons in its valence shell. The three electrons are used to form three single covalent bonds with three hydrogens. Therefore one unshared pair of valence electrons is present on the nitrogen atom in an ammonia molecule.
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