Which of the following DO NOT contribute to hardness of water?
(A) K+ (B) Na+ (C) Ca2+ (D) Mg2+ (E) Fe3+
Choose the correct answer from the options given below:

Correct option is A

1. Hardness of Water:
· Hardness of water is caused by the presence of divalent or trivalent cations, such as Ca2+, Mg2+, and Fe3+. These ions react with soap and form insoluble precipitates, leading to "hardness."
2. Contributors to Hardness:
· Ca2+ : A primary contributor to water hardness, typically from dissolved calcium salts (e.g., calcium carbonate).
· Mg2+ : Another major contributor, usually from magnesium salts.
· Fe3+ : Contributes to hardness if present in water as it forms insoluble hydroxides and carbonates.
3. Non-Contributors to Hardness:
· K+ (Potassium): Does not contribute to hardness as it is monovalent and highly soluble.
· Na+ (Sodium): Also monovalent and does not form insoluble precipitates with soap. Sodium salts are associated with soft water.
Information Booster: 1. Types of Hardness:
· Temporary Hardness: Caused by bicarbonates of Ca2+ and Mg2+. Can be removed by boiling.
· Permanent Hardness: Caused by sulfates and chlorides of Ca2+, Mg2+, and Fe3+. Cannot be removed by boiling.
2. Monovalent vs. Divalent Ions:
· Monovalent ions (K+) do not contribute to hardness.
· Divalent or trivalent ions (Ca2+, Mg2+, Fe3+) contribute to hardness.
3. Applications:
· Understanding hardness is critical for water treatment, boiler maintenance, and preventing scaling in pipelines.
Thus, K+ and Na+ do not contribute to the hardness of water.