Valency

Correct answer:

Explanation:
The valency of sodium (Na) is 1, meaning each sodium atom can donate 1 electron.
The valency of oxygen (O) is 2, meaning each oxygen atom needs 2 electrons to complete its octet.

To balance the charges, 2 sodium atoms (each donating 1 electron) are needed to bond with 1 oxygen atom (which needs 2 electrons).

Hence, the correct chemical formula is: .

The number of electrons gained by a non-metallic element to achieve a stable electron configuration (octet rule) is equal to its valency. Valency is the combining capacity of an element, which is determined by the number of electrons it needs to gain, lose, or share to achieve a full outer electron shell.