This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
[{'content': 'Which of the following do not cause hardness of water? \nSelect and explain. \nA. Calcium carbonate, B. Calcium sulfate, C. Calcium bicarbonate, D. Magnesium bicarbonate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a. Calcium carbonateRef: Parks Text book of Preventive and Social Medicine, 24th Ed; Page No-763Hardness is defined as soap destroying power of water.Hardness is mainly due to 4 dissolved compounds:Calcium bicarbonateCalcium sulfateMagnesium bicarbonateMagnesium sulfateOther compounds responsible for hardness are chlorides and nitrates of calcium and magnesium and iron, manganese, aluminium compounds to a small extent.There are 2 types of hardness:Temporary hardness: Due to carbonates of Ca and MgPermanent hardness: Due to sulphate, chloride and nitrates of Ca and Mg', 'role': 'assistant'}]