Hardness of water is mainly caused by the presence of dissolved salts of:
A. Copper and Lead
B. Iron and Zinc
C. Calcium and Magnesium
D. Sodium and Potassium
Answer: Option C
Solution (By JKExamLibrary)
Water hardness is primarily caused by the presence of dissolved multivalent cations, most commonly calcium (Ca²⁺) and magnesium (Mg²⁺) ions, usually in the form of bicarbonates, chlorides, or sulfates. Sodium and potassium salts do not cause hardness.
Explanation:
CH₄ + 2O₂ → CO₂ + 2H₂O + heat. Complete combustion of any hydrocarbon with sufficient oxygen always produces carbon dioxide and water. Incomplete combustion due to limited oxygen produces carbon monoxide (CO) and/or soot (carbon particles). Methane is the main component of natural gas and biogas. CO is a poisonous gas. The combustion of alkanes is highly exothermic.
Explanation:
Combination: two or more reactants combine to one product. Mg and O₂ combine to form MgO. A is decomposition; B is displacement; D is double displacement.
Explanation:
Soap (sodium carboxylate) reacts with Ca²⁺ and Mg²⁺ ions present in hard water to form an insoluble precipitate known as scum. This reduces lathering and wastage of soap. Synthetic detergents do not form scum because their calcium/magnesium salts are soluble.
No comments yet. Be the first to start the discussion!