Answer : 3. "Wasshing soda"
Explanation :

Answer: C) Wasshing soda Explanation: Hardness can be removed by adding sodium carbonate (washing soda) or by passing the water through an ion-exchange column.   Hardness in water is caused by dissolved magnesium ions and calcium ions. These can get into the water when it comes into contact with limestone and other rocks that contain calcium compounds. This can happen, for example, when rainwater flows over these rocks on its way to a reservoir.   Hardness in water is of two types. They are : 1. Temporary hardness 2. Permanent hardness   1. Temporary hardness:: Temporary hardness is caused by dissolved calcium hydrogen carbonate. 2. Permanent hardness:: Permanent hardness is caused by dissolved calcium sulfate. Unlike temporary hardness, it is not removed by boiling the water.