Most metal oxides are insoluble in water but some of these dissolve in water. What
are these oxides and their solutions in water called?

Dear student
Yes most metal oxides are insoluble in water, but some of these dissolve in water
Sodium oxide and Potassium oxide dissolve in water . These solutions in water are called Alkalis.

Na₂O (s) +H₂O(l) $\to$     2NaOH(aq)
K₂O(s) +H₂O(l)     $\to$   2KOH(aq)

Regards