Which one among the following has valency of 3 ?

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 (usually an octet).

• Nitrogen (N): With an atomic number of 7, its electronic configuration is 2, 5. It has 5 electrons in its outermost shell and needs 3 more to complete its octet. Thus, its valency is 3.
• Carbon (C): Atomic number 6 (configuration 2, 4) has a valency of 4.
• Oxygen (O): Atomic number 8 (configuration 2, 6) needs 2 electrons to complete its octet, giving it a valency of 2.
• Sodium (Na): Atomic number 11 (configuration 2, 8, 1) loses 1 electron to achieve stability, resulting in a valency of 1.

Hence, among the given options, Nitrogen is the element with a valency of 3.