The valency of nitrogen in NO₂ is: MCQ with Answer and Explanation

Explanation:
Heating coal in the absence of air (destructive distillation) produces coke (solid residue, high carbon), coal tar (mixture of aromatic compounds), ammoniacal liquor, and coal gas (H₂, CH₄, CO). Coke is used in blast furnace. Coal tar is a source of aromatic chemicals and pitch. Coal gas was used for lighting historically.

Explanation:
Henry Moseley established that the properties of elements are periodic functions of their atomic numbers, not atomic masses. This refined Mendeleev's table and resolved anomalies like Ar-K. The modern periodic table is thus based on Moseley's work. Mendeleev proposed the original table based on atomic masses. Newlands gave Law of Octaves. Meyer plotted atomic volume curve.

Explanation:
Limestone (CaCO₃) decomposes to CaO, which is a basic flux. It reacts with the acidic impurity silica (SiO₂) to form calcium silicate (CaSiO₃), a fusible slag: CaO + SiO₂ → CaSiO₃. Slag floats on molten iron and is tapped separately. Reduction is done by CO/coke. Flux makes gangue removal easier. Slag is used in cement, road building.