Which one is water soluble oxide?
A. Al2O3
B. Na2O
C. PbO
D. CuO
Also give reason for your answer

Dear Student,
Among Al2O3, Na2O, CuO, and PbO - Na2O is a water-soluble oxide. (OPTION B)
Na2O + H2 2NaOH (strong base and hence water soluble)
Other oxides are not water-soluble because,
In Al2O3, Al is in a +3 oxidation state hence has high polarising power
In CuO, Cu is present in +2 oxidation state and is a transition metal
while in PbO, Pb is present in the +2 oxidation state and is the last member of the carbon family due to which it shows lanthanide contraction.
These facts lead to the more covalent character in these oxides.
Hence they are less soluble to insoluble in water

Regards

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