pH1>pH2=pH3>pH4
pH1<pH2<pH3<pH4
pH1<pH2<pH3=pH4
pH1>pH2>pH3>pH4
When the above compounds are dissolved in water, each forms their respective bases. As the basicity of these oxides decreases, when placed in water, the basicity of the solution also decreases.
Na₂O + 2H₂O → 2NaOH + H₂O
Na₂S + 2H₂O → 2NaOH + H₂S
Na₂Se + 2H₂O → 2NaOH + H₂Se
Na₂Te + 2H₂O → 2NaOH + H₂Te
The order of neutralization of NaOH is:
H₂Te > H₂Se > H₂S > H₂O
Hence their aqueous solutions have the following order of basic character due to neutralization of NaOH with H₂O, H₂S, H₂Se, H₂Te:
Na₂O > Na₂S > Na₂Se > Na₂Te.