The correct order of pH of isomolar solution in sodium oxide
(pH1), sodium sulphide \left(\mathrm{pH}_2\right)
,sodiumselenide(pH3)andsodiumtelluride(pH4) is
pH1>pH2>pH3>pH4 because in aqueous solution, they are hydrolysed as follows.
Na2O+2H2O⟶ Base 2NaOH+H2ONa2 S+2H2O⟶ Strong base 2NaOH+ Weak acid H2 SNa2Se+2H2O⟶ Strong base 2NaOH+H2Se Weak acid Na2Te+2H2O⟶ Strong base 2NaOH+H2Te Weak acid
Order of acidic strength
H2Te>H2Se>H2 S>H2O
Order of neutralisation of NaOH
H2Te>H2Se>H2 S>H2O
Hence, their aqueous solutions have the following order of basic character due to neutralisation of NaOH with
H2O,H2 S.H2SeandH2TeNa2O>Na2 S>Na2Se>Na2Te(∴pH of basic solution is higher than acidic or least basic solution.)