Which salt is used to remove the permanent hardness of water?

Correct option is C

The correct answer is (c) Na2CO3 . 10H2O. Sodium carbonate decahydrate, also known as washing soda, is used to remove permanent hardness of water. It works by precipitating calcium and magnesium ions, which cause hardness, as their insoluble carbonates, thereby softening the water.
Important Key Points:
· Sodium carbonate Na2CO3 . 10H2O is effective in softening hard water.
· It removes permanent hardness by precipitating calcium and magnesium as carbonates.
· Washing soda is widely used in laundry detergents for this reason.
· Permanent hardness is caused by the presence of calcium and magnesium salts in water.
· Softening water is essential in preventing scale formation in pipes and boilers.
· Understanding water hardness is important in industrial processes and everyday life.