\({H_2}Te > {H_2}Se > {H_2}S > {H_2}O\)
\(N{a_2}O\) is a salt of \(NaOH + {H_2}O\)and \({H_2}O\) is least acidic among given acidshence \(pH\) in this case will be \({\max ^m}\).
$NH_3$ + $H_2O$ $\rightleftharpoons$ $NH_4^ + + O{H^ - }$
$[$આપેલ : પાણીમાં $Ca ( OH )_{2}$ નો દ્રાવ્યતા ગુણાકાર $=5.5 \times 10^{-6}$ છે.$]$