The correct order of pH of isomolar solution in sodium oxide (pH10 sodium sulphide (pH2), sodium selenide (pH3) and sodium telluride (pH4) is pH1>pH2>pH3>pH4 because in aqueous solution, they are hydrolysed as follows
Na2O+2H2O→
2NaOH
Strongbase
+
H2O
water
Na2S+2H2O→
2NaOH
Strongbase
+
H2S
weakacid
Na2Se+2H2O→
2NaOH
Strongbase
+
H2Se
weakacid
Na2Te+2H2O→
2NaOH
Strongbase
+
H2Te
weakacid
Order of neutralisation of NaOH H2Te>H2Se>H2S>H2O Order of acidic strength H2Te>H2Se>H2S>H2O Hence, their aqueous solutions have the following order of basic character due to neutralisation of NaOH with H2O,H2S,H2Se and H2Te. Na2O>Na2S>Na2Se>Na2Te (∴ pH of basic solution is higher than acidic or least basic solution).