Which one of the following tests employs Ethylene Diamine Tetra Acetic Acid (EDTA) as a titrating agent?

Option 3 : Hardness

Explanation:

Hardness is caused by polyvalent metallic cations, though the divalent cations, such as calcium and magnesium cations are usually the predominant cause of hardness. In addition, hardness is also caused by Fe²⁺ and Mn²⁺ ions.

Hardness is normally expressed in terms of CaCO₃. 

• The most widely used method its determination is by using,
• Titrant in hardness test: EDTA (Ethylene di-amine tetra acetic acid)
• The titration is done by adding a small amount of buffer (pH 10) followed by the addition of Eriochrome black T (EBT) as an indicator.