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The hardness of a water sample is measured directly by titration with $\text{0.01 M}$ solution of ethylenediamine tetraacetic acid $\text{(EDTA)}$ using eriochrome black $\text{T (EBT)}$ as an indicator. The $\text{EBT}$ reacts and forms complexes with divalent metallic cations present in the water. During titration, the $\text{EDTA}$ replaces the $\text{EBT}$ in the complex. When the replacement of $\text{EBT}$ is complete at the end point of the titration, the colour of the solution changes from

1. blue-green to reddish brown
2. blue to colourless
3. reddish brown to pinkish yellow
4. Wine red to blue

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