Concept:Valency is the combining capacity of an element. It is measured by the number of hydrogen atoms it can combine with or displace to form a compound.
Explanation:Carbon (C) has a valency of 4 because it forms four covalent bonds to achieve a stable octet (e.g.,
CH4​).
Oxygen (O) has a valency of 2 because it needs two electrons to complete its outer shell (e.g.,
H2​O).
Nitrogen (N) has a valency of 3 because it needs three electrons to complete its outer shell (e.g.,
NH3​).
Sodium (Na) has a valency of 1 because it loses one electron to achieve a stable configuration (e.g.,
NaCl).
Among these, only nitrogen shows a valency of 3.
Answer:Nitrogen