Which one of the following elements has valency three ?

Valency is the combining capacity of an atom, determined by the number of electrons it must gain, lose, or share to achieve a stable electronic configuration [t1][t3]. Boron (atomic number 5) has three electrons in its outermost shell, giving it a valency of three [t1][t2][t6]. In contrast, Lithium (atomic number 3) has one valence electron and a valency of one [t1][t4]. Oxygen (atomic number 8) has six valence electrons and requires two more to complete its octet, resulting in a valency of two [c4][t1]. Carbon (atomic number 6) has four valence electrons and is tetravalent, meaning it has a valency of four [c1][t10]. Therefore, among the given options, Boron is the element with a valency of three [t2][t7].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.2 VERSATILE NATURE OF CARBON > p. 62
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 60