Which of the following indicator used in determination of hardness?

Correct option is A

The correct answer is (a) EBT

Explanation:

• EBT stands for Eriochrome Black T, a complexometric indicator.
• It is used in the EDTA titration method to determine the total hardness of water.
• Hardness is caused by the presence of Calcium ($Ca^{2+}$) and Magnesium ($Mg^{2+}$) ions.
• EBT forms a wine-red complex with these metal ions.
• As EDTA is added, it displaces EBT, and at the endpoint, the solution turns from wine-red to steel blue.

• The titration is usually performed at a pH of 10 using an ammonia buffer.
• Water hardness is typically expressed in terms of $CaCO_3$ equivalents.

• Used for acid-base titrations; turns pink in basic solutions.

• Used for acid-base titrations; turns red in acidic and yellow in basic solutions.