Read the passage carefully and answer the questions
The coordination compounds are of great importance. These compounds are widely present in the mineral, plants and animal world and are known to play many important functions in the area of analytical chemistry, metallurgy, biological systems, industry and medicine. For example, coordination compounds find use in many qualitative and quantitative chemical analysis. Some important metal extraction and purification make use of complex formation. Hardness of water can be estimated by stable complex formation of Ca\(^2+\) and Mg\(^2+\)
Hardness of water can be estimated by titration with _________ .

1. A sodium salt of \(\alpha\)-nitroso- \(\beta\)-naphthol
2. B Nickel salt of DMG
3. C sodium salt of EDTA
4. D copper salt of cupron