Assertion (A): At absolute zero, the volume of an ideal gas becomes zero. Reason (R): At absolute zero, the kinetic energy of the gas molecules is zero. MCQ with Answer and Explanation

Explanation:
Dmitri Mendeleev proposed the periodic law based on atomic mass. However, anomalies arose. In 1913, Henry Moseley discovered that the atomic number (number of protons) is the fundamental property. He proposed the modern periodic law: the properties of elements are periodic functions of their atomic numbers.

Explanation:
Steel is an alloy of iron with controlled amounts of carbon (0.02-2.1%) and often other elements like manganese, chromium, nickel, etc. Cast iron contains 2-4% carbon. In steelmaking (Bessemer, LD process), impurities like excess carbon, silicon, manganese, sulfur, phosphorus are oxidized and removed, then desired carbon and alloying elements are added to achieve specific properties.

Explanation:
Cathode (negative electrode): 2H₂O + 2e⁻ → H₂ + 2OH⁻ (or 2H⁺ + 2e⁻ → H₂). Hydrogen gas is collected at the cathode. At the anode, oxygen is produced: 2H₂O → O₂ + 4H⁺ + 4e⁻. The volume of H₂ is double that of O₂.