Answer:
The correct options are: 1. Ca²⁺ and 4. Mg²⁺
Step-by-step explanation:
Hard water is the water with high mineral content. Temporary hardness and permanent hardness are the two types of hardness of water.
Temporary hardness is due to the presence of dissolved bicarbonate minerals. These minerals present in the water, dissociate to give multivalent calcium cations (Ca²⁺) and magnesium cations (Mg²⁺).
Therefore, the presence of metal cations such as calcium cations (Ca²⁺) and magnesium cations (Mg²⁺) makes the water hard.