The question said that the substance was malleable without specifying whether it was a soft or hard substance. Also, the rate at which the oxide would dissolve obviously depends on factors such as temperature and the volume of water used to dissolve it. The word “slowly” in the question does not say anything about the conditions under which the oxide was dissolved. So, I am still convinced that the metal is either a group I or group II metal.
Anyone has a better answer and would like to share it?
Thanks.