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# What is the correct relationship between the $pH$s of isomolar solutions of sodium oxide ($pH_1$), sodium sulphide ($pH_2$), sodium selenide ($pH_3$) and sodium telluride ($pH_4$)?

(a) $pH_1 > pH_2 = pH_3 > pH_4$

(b) $pH_1 < pH_2 < pH_3 < pH_4$

(c) $pH_1 < pH_2 < pH_3 \approx pH_4$

(d) $pH_1 > pH_2 > pH_3 > pH_4$

Toolbox:
• Acidic character increases in the order $H_2O < H_2S < H_2Se < H_2Te$

Answer: $pH_1 > pH_2 > pH_3 > pH_4$

Acidic character increases in the order $H_2O < H_2S < H_2Se < H_2Te$

Basic character of conjugate bases will be in the order
$O^{2-} > S^{2-} > Se^{2-} > Te^{2-}$

More the basic character, more the $pH$

$\therefore pH$s are in the order
$pH_1 > pH_2 > pH_3 > pH_4$