Which of the following fuels has the highest calorific value? MCQ with Answer and Explanation

Explanation:
Calcium (Ca²⁺) and magnesium (Mg²⁺) ions react with soap anions to form insoluble precipitates (scum), preventing lather. Sodium and potassium soaps are soluble and lather well. So detergents are preferred in hard water because their calcium/magnesium salts are soluble. Hardness is measured in terms of CaCO₃ equivalent.

Explanation:
Mass is an extensive property, meaning it depends on the quantity of matter. Density, boiling point, and refractive index are intensive properties that remain constant regardless of the amount of substance. Intensive properties are useful for identifying substances. For example, pure water boils at 100°C at 1 atm irrespective of whether you have 10 mL or 10 L. Exam trick: Extensive properties like mass, volume, and length add up when you combine samples; intensive properties do not.

Explanation:
Lower activation energy means more molecules have energy to cross the barrier, increasing the reaction rate. Enthalpy (ΔH) and equilibrium constant remain unchanged. Catalyst does not affect stoichiometry.