Which of the following is an extensive property of matter? MCQ with Answer and Explanation

Explanation:
Calcination involves heating an ore in limited supply or absence of air, often to convert carbonates/hydroxides to oxides and remove moisture or volatile impurities. Example: CaCO₃ → CaO + CO₂; Al(OH)₃ → Al₂O₃ + 3H₂O. Roasting is heating in excess air, usually for sulfide ores. Smelting uses reducing agents to obtain metal. Leaching uses chemicals.

Explanation:
Rhizobium bacteria form root nodules in leguminous plants (peas, beans, clover) and fix atmospheric N₂ into ammonia, providing nitrogen to the plant, while the plant supplies carbohydrates. Azotobacter and Azospirillum are free-living nitrogen fixers. Pseudomonas is a general soil bacterium. Symbiotic association is mutualistic. Inoculating seeds with Rhizobium culture increases soil fertility.

Explanation:
Bakelite is a thermosetting phenol-formaldehyde resin with excellent heat resistance and electrical insulation properties, making it suitable for switches, handles, and electrical fittings. Polythene and PVC are thermoplastics that soften on heating. Polystyrene is brittle and not highly heat resistant. Thermosets do not melt upon reheating.