Three elements Na, S and O combine to form a compound Na2SOg. What is the valency of S in this compound?

The compound Na2SO4 (sodium sulfate) consists of sodium, sulfur, and oxygen. To determine the valency (oxidation state) of sulfur, we apply the rule that the sum of oxidation states in a neutral compound must be zero. Sodium (Na) is a Group 1 metal with a valency of +1 [1]. Oxygen (O) typically has a valency of -2. In Na2SO4, there are two sodium atoms and four oxygen atoms. The calculation is: 2(+1) + S + 4(-2) = 0, which simplifies to 2 + S - 8 = 0, resulting in S = +6. Therefore, sulfur exhibits a valency of 6+ in this compound. This is consistent with sulfur's ability to expand its octet and form six bonds in the sulfate radical.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 46