Explain why the anion solutions were prepared using sodium salts rather than calcium salts?

Anion solutions are those which allows dissociations of negatively charged atoms in the water or any liquid. In essence, the sodium salts are used for the preparation due to the higher activity of sodium salts.

This is because, sodium salts will dissociate into Na⁺ and the counterpart ion while calcium dissociates into Ca²⁺. As it is seen in the charges of the atoms, sodium is more reactive because it is easier for atoms to lose 1 electron than two.