A metal M readily forms its sulphate MSO4 which is water-soluble. It forms its oxide MO which becomes inert on heating. It forms an insoluble hydroxide M(OH)2 which is soluble in NaOH solution. Then M is

  1. Mg
  2. Be
  3. Ba
  4. Ca


On moving down, water solubility of alkaline earth metals decreases.

Oxides and hydroxides of alkaline earth metal are basic except Be which is amhoteric.

Hence, the metal is Be.

The correct option is B.