Answer:
B. Soap solution
Step-by-step explanation:
Hardness of water refers to the degree of calcium and magnesium in the water. In other words, hard water contains excessive mineral contents. The degree of hardness of a water body can be measured using the SOAP TEST KIT.
Due to the formation of insoluble minerals, soap forms an exvessive substance in the presence of hardwater because the particles or minerals contained in the water is reacting to form something insoluble. Hence, a SOAP test kit can be used to test the hardness of water.