This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'Hardness of water is expressed per litre (m Eq/L), one unit which is equivalent to which one of the following. \nSelect and explain. \nA. 20 mg CaCO3 (20 ppm), B. 30 mg CaCO3 (30 ppm), C. 40 mg CaCO3 (40 ppm), D. 50 mg CaCO3 (50 ppm)', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Hardness of water\n\nHardness of water is defined as the soap-destroying power of water.\nWater is considered to be bard if large amounts of soap are required to produce lather.\nThe hardness is caused by high mineral content, Mainly calcium and magnesium cations.\nHardness may be : -\n\ni) Temporary (Carbonate) hardness → Calcium bicarbonate & Magnesium bicarbonate.\n\nIt is called temporary because it can be removed by boiling or addition of lime.\n\nii) Permanent (Non-Carbonate) hardness → Calcium Sulfate, magnesium sulfate, Calcium chloride, magnesium chloride.\n\nIt is called permanent because it cannot be removed by boiling.\nHardness is expressed in terms of mili-equilents per litre (mEq/L).\nOne mEq/L of hardness - producing ion is equal to 50 mg CaCO3 (50ppm) in one litre of water.', 'role': 'assistant'}]