Question

The alums used for purifying water are:

• A. ferric alum
• B. chrome alum
• C. potash alum
• D. ammonium alum

Answer 1

Answer: (C), (D)

The correct options are
C potash alum
D ammonium alum

When Potash alum and Ammonium alum are added to water, they dissociate and form ions (charged atoms). Suspended colloidal particles (Dirt particles) with negative surface charges (like clay and bacteria) bind together with these ions and become heavy enough to settle to the bottom of the water. The process is known as flocculation.

Hence, the correct options are $\text{C}$ and $\text{D}$