जल की स्थायी कठोरता को निम्नलिखित में से किस प्रक्रिया द्वारा दूर किया जा सकता है?

Which chemical is commonly added to municipal water to kill bacteria?

What primary function does Alum (Potash Alum) serve in the water purification process?

Which one of the following methods is used to remove permanent hardness of water?