Dmitri Mendeleev's periodic table was based on: MCQ with Answer and Explanation

Explanation:
Electrolysis of water splits it into hydrogen and oxygen, it is not a purification method but a decomposition. Reverse osmosis uses semipermeable membrane to remove ions and impurities. UV irradiation kills microorganisms. Distillation boils water and condenses steam, removing non-volatile impurities. Other methods: filtration, chlorination, ozonation, boiling.

Explanation:
Vulcanization involves heating natural rubber with sulfur, forming cross-links between polymer chains. This improves elasticity, tensile strength, and resistance to temperature changes. Hydrogenation adds H₂, saponification makes soap, fermentation produces alcohol.

Explanation:
Uranium (U) is a naturally occurring heavy metal that is radioactive. Its most common isotopes are U-238 and U-235. Aluminum, iron, and calcium are stable, non-radioactive elements under normal conditions, though they may have synthetic radioactive isotopes.