WZ_ASRJC
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What is the approach for this question?
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BedokFunlandJC
X is Mg (since Na+ doesn't hydrolyse significantly, Al3+ hydrolyses completely ; and MgO is the only Group 2 oxide that is slightly soluble).
Y is S, as S forms SO2 or SO3, and BaSO3(s) and BaSO4(s) are both considered insoluble (or sparingly soluble).
Write separate equations for the hydrolyses of SO2 and SO3, and determine via calculations whether the white ppt is BaSO3(s) or BaSO4(s).
Both H2SO3(aq) and H2SO4(aq) are diprotic acids, hence either will exactly neutralize the same amount of diprotic base MgO(s), even though the resulting salt solution will be slightly acidic (and not neutral as wrongly stated in the question), due to the slight hydrolysis of the Mg2+(aq), and negligible hydrolysis of the sulfite or sulfate anion.
Comparing melting points, describe strength of metallic bonding versus van der Walls intermolecular interactions (even though sulfur has an unusually high melting point for a simple molecular species due to its large molecular size).

Btw WZ_ASRJC, so far when you post your tutorial qns, you didn't include the source (eg. TYS 2012 P3 Q2, SRJC 2013 P2 Q3, etc). If the source is given in the question, do remember to include it. 
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