In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.
Q: Question: In the determination of water hardness due to the presence of Ca2 + and Mg2 + ions, the titrant reagent is used:
Options: <0> Methyl orange. <1> A standard solution of potassium chloride. <2> Black Eriochrome T. <3> A standard solution of ethylenediaminetetraacetic acid (EDTA). <4> A solution of AEDT previously standardized against a solution of potassium phthalate.
A:
chemistry