Identify the principal causes of acidity in water supplies (choose the most complete statement).

Introduction / Context:
Acidity in water is due to free mineral acids, dissolved carbon dioxide, and hydrolyzing metal salts that generate acidic species. Understanding sources helps in choosing appropriate neutralization or corrosion-control strategies.

Given Data / Assumptions:

• Typical raw waters and chemically treated waters (e.g., alum coagulation).
• Standard definition of acidity as the capacity to neutralize bases.

Concept / Approach:
Free CO2 forms carbonic acid in water. Mineral acids (e.g., H2SO4, HCl) directly contribute to acidity. Certain metal salts (FeSO4, Al2(SO4)3) hydrolyze to produce acidic conditions (e.g., forming H+ via hydrolysis), increasing acidity until alkalinity neutralizes them.

Step-by-Step Solution:

Verification / Alternative check:
Standard water chemistry texts describe titratable acidity components including CO2 and hydrolysis products of alum/iron salts.

Why Other Options Are Wrong:

• Each partial listing omits other well-known contributors to acidity; therefore incomplete.

Common Pitfalls:

• Equating acidity solely with free mineral acids and ignoring CO2 or salt hydrolysis.

Final Answer:
All of the above