The temporary hardness of water is caused by the presence of: MCQ with Answer and Explanation

Explanation:
Light catalyzes decomposition of H₂O₂. Dark bottles (amber) block light, stabilizing it. Often a stabilizer like urea or phosphoric acid is added. Metal containers may catalyze decomposition.

Explanation:
Chemical properties describe a substance's ability to undergo chemical changes—reactivity with acid, flammability, oxidation states, etc. Melting point, density, boiling point are physical properties that can be observed without changing composition. Reactivity with acid involves formation of new substances. A piece of magnesium reacting with HCl is a chemical change.

Explanation:
HF has a polar covalent bond due to large electronegativity difference between H (2.1) and F (4.0), causing unequal sharing. It is not ionic because the difference is not extreme enough (>1.7 is typical but borderline). The bond is polar.