In all the compounds of calcium (Ca) listed, the valency of the metal is +2. Now, the element barium (Ba) belongs to the same group as calcium. It must be also divalent in its compounds. The formulae of the respective compounds of the element are :
`underset(("Barium oxide"))(BaO)" "underset(("Barium hydroxide"))(Ba(OH)_(2))" "underset(("Barium sulphate"))(BaSO_(4))`