When hard water is evaporated completely, the white solid remains in the container. It may be due to the presence of 1. Carbonates of Ca and Mg 2. Sulphates of Ca and Mg 3. Chlorides of Ca and Mg Select the correct answer using the code given below :

Hardness in water is primarily caused by the presence of dissolved bicarbonates, chlorides, and sulphates of calcium and magnesium [2]. When hard water is evaporated completely, these dissolved minerals remain as a white solid residue. Temporary hardness is caused by bicarbonates, which upon heating or evaporation, decompose into insoluble carbonates (CaCO3) or hydroxides (Mg(OH)2), forming a solid scale [1]. Permanent hardness is attributed to the presence of chlorides (CaCl2, MgCl2) and sulphates (CaSO4, MgSO4) of calcium and magnesium [2]. Unlike bicarbonates, these salts do not decompose upon boiling but remain in the container as solid mineral matter once the solvent (water) is entirely removed through evaporation [2]. Therefore, the white solid residue consists of carbonates, sulphates, and chlorides of calcium and magnesium.

Sources

1. [1] https://annamalaiuniversity.ac.in/studport/download/engg/chemistry/resources/Chemistry_19_ETBS202_2020_II_semester.pdf
2. [2] https://www.uptti.ac.in/classroom-content/data/Unit-1_Water%20and%20its%20treatment.pdf