JEE Main · 2021 · 22 Jul 2021 · Shift 2 · s-Block Elements

Barium is the alkaline earth metal of the sixth period, so its outer configuration is $6s^2$. Calcium oxalate is the salt that separates out when oxalate is added to a calcium solution, being insoluble in water. Lithium gives the smallest and most polarising cation of its group, so its compounds have appreciable covalent character and dissolve in organic solvents. Sodium hydroxide is fully ionised and supplies one hydroxide ion per formula unit, making it a very strong monoacidic base. The pairing is barium with the $6s^2$ outer configuration, calcium with the water-insoluble oxalate, lithium with organic solvent soluble compounds and sodium with the very strong monoacidic base.