An alkaline earth metal (M) gives a salt with chlorine, which is soluble in water at room temperature. It also forms an insoluble sulphate whose mixture with a sulphide of a transition metal is called 'lithopone' -a white pigment. Metal M is :

A salt with chlorine that is insoluble in water at room temperature but soluble in boiling water is produced by an alkaline earth metal (M). Additionally, it produces an insoluble sulphate, known as lithopone, a white pigment, when combined with a transition metal's sulphide. Ba is the metal M.Barium chloride, or BaCl₂, is the chlorine-containing salt.
Barium sulphate, or BaSO₄, is the insoluble sulphate. When solutions of barium sulphide and zinc sulphate are combined, a precipitate known as lithopone, an insoluble combination of the two substances, forms. Filtration is used to recover the precipitate, which is subsequently calcined (roasted) at temperatures exceeding ${600}^{\circ }\mathrm{C}\text{. }$