Assertion `(A)`: Hardness of water is determined by titrating it with disodium salt of `EDTA`.
Reason `(R)` :The indicator used in the titration is Eriochrome Black`-T` at `pH=10`.
A. If both (A) and (R) are correct and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct but (R) is not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect, but (R) is correct.