A metal M readily forms its sulphate MSO4 which is water soluble. It forms its oxide MO which becomes inert on heating. It forms its insoluble hydroxide MOH2 which is soluble in NaOH solution. Then M is

Be forms highly soluble BeSO4 , It forms oxide which becomes inert on heating.Be forms water insoluble Be(OH)2 which dissolves in NaOH solution to form sodium beryllate(Na2BeO2)The solubility of hydroxides of alkaline earth metals in water increases on moving down the group.