It's not accurate to talk about the "valency" of a compound like sodium sulfate (Na₂SO₄).

Here's why:

* Valency refers to the combining capacity of an element. It's the number of electrons an atom can gain, lose, or share to form chemical bonds.

* Sodium sulfate is a compound, meaning it's formed by the combination of two or more elements.

Instead of valency, we talk about the ionic charges of the individual ions that make up sodium sulfate:

* Sodium (Na) has a valency of +1, meaning it loses one electron to form a positively charged ion (Na⁺).

* Sulfate (SO₄) has a valency of -2, meaning it gains two electrons to form a negatively charged ion (SO₄²⁻).

The overall compound is neutral because the two sodium ions (2 x +1 = +2) balance the charge of the sulfate ion (-2).