Explanation:

Given that Chemical formula of the sodium salt of given anion X is Na2X. We know that sodium is a single ionized atom so; it can lose only one electron from its ground state. So oxidation state of sodium ion in salt is +1. Then, +1×2+y=0 2+y = 0 y = - 2 Oxidation state of anion is -2. Now the chemical formula of an aluminium salt is, Oxidation state of aluminium is +3 Then +3×r + (-2)×q = 0 3r = 2q r/q = 2/3 So, the chemical formula will be Al2X3