Q.Which compound is named as "Blue John" among the following compounds?

For alkaline earth metals, M²⁺ is the sole oxidation state; their compounds are predominantly ionic, though less so than the alkali metals' (greater nuclear charge, smaller size).

Oxides: monoxides from heating the metal in O₂; BeO and MgO are nearly insoluble, the rest form hydroxides. Basicity: BeO amphoteric, MgO weakly basic, CaO/SrO/BaO strongly basic; BeO is covalent (small Be²⁺), the rest ionic. Every metal except Be also forms a peroxide (2BaO + O₂ → 2BaO₂).

Hydroxides: MO + H₂O → M(OH)₂ (every oxide except BeO); solubility, thermal stability and basicity all rise down the group, though still less than the alkali metal hydroxides. Be(OH)₂ is the exception -- amphoteric, reacting with both acid and base (Be(OH)₂ + 2NaOH → Na₂BeO₂ + 2H₂O; Be(OH)₂ + 2HCl → BeCl₂ + 2H₂O). …