What is the definition of noncarbonate hardness (NCH)?

Noncarbonate hardness (NCH) refers specifically to the portion of hardness in water that is not associated with carbonate ions. Hardness in water typically arises from the presence of divalent metal ions, primarily calcium (Ca²⁺) and magnesium (Mg²⁺). This hardness can be categorized into two types: carbonate hardness and noncarbonate hardness.

Carbonate hardness is related to the presence of bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻) ions, which can precipitate with calcium and magnesium ions. These ions can be removed through the process of lime softening or other treatments. Noncarbonate hardness, on the other hand, encompasses all the hardness contributed by calcium and magnesium ions that exist as sulfates (SO₄²⁻), chlorides (Cl⁻), and nitrates (NO₃⁻). It does not involve the carbonate and bicarbonate ions, which means it remains even after treatment methods aimed at reducing carbonate hardness.

Therefore, recognizing that noncarbonate hardness is solely about the portion of hardness linked to ions other than carbonates solidifies the understanding that option B accurately captures its definition.