In chemical terms, what are alums used for purifying water for drinking purposes ? A. Hydrated chlorides B. Double nitrate C. Double sulphates D. Nitrates of aluminium

The correct answer is C. Double sulphates.

Alum is a generic term for a group of double sulfates of aluminum and potassium, or aluminum and ammonium. They are used in a variety of applications, including water purification. Alum is effective in purifying water because it forms a precipitate with impurities in the water, such as bacteria and viruses. This precipitate can then be filtered out, leaving

Option A is incorrect because alum is not a hydrated chloride. A hydrated chloride is a compound that contains chlorine and water. Alum does not contain chlorine.

Option B is incorrect because alum is not a double nitrate. A double nitrate is a compound that contains two nitrate ions. Alum does not contain two nitrate ions.

Option D is incorrect because alum is not a nitrate of aluminum. A nitrate of aluminum is a compound that contains aluminum and nitrate ions. Alum does not contain aluminum and nitrate ions.