Which term describes water hardness?

• A. Alkalinity
• B. Conductivity
• C. Hardness
• D. Turbidity

Answer: (C)

The concept being tested is how we name a specific characteristic of water quality. Water hardness specifically refers to the concentration of minerals, mainly calcium and magnesium ions, dissolved in water. These minerals cause scale buildup in pipes and appliances and affect how well soap lathers. This distinguishes hardness from other water terms: alkalinity is about buffering capacity from bicarbonate, carbonate, and hydroxide ions; conductivity measures how easily electricity runs through all dissolved ions (not just hardness); turbidity is about cloudiness from suspended particles. So hardness is the correct term because it directly describes those calcium and magnesium minerals in the water.