Which of the following pairs are isobars? MCQ with Answer and Explanation

Explanation:
Rusting involves anodic oxidation of iron (Fe → Fe²⁺ + 2e⁻) and cathodic reduction of oxygen (O₂ + 2H₂O + 4e⁻ → 4OH⁻) in the presence of water acting as electrolyte. CO₂ can form carbonic acid accelerating it, but not required. Nitrogen is inert. High temperature alone doesn't cause rusting without moisture and oxygen.

Explanation:
Boyle's law: P ∝ 1/V or PV = constant at constant T and n. So if volume increases, pressure decreases. This is because gas molecules have more space and hit the walls less frequently. An example is a syringe: pulling the plunger increases volume, decreases pressure.

Explanation:
Plaster of Paris is calcium sulfate hemihydrate, CaSO₄·½H₂O. It is obtained by heating gypsum (CaSO₄·2H₂O) at 373 K. It sets to a hard mass on mixing with water reforming gypsum. Option B (2CaSO₄·H₂O) is equivalent to CaSO₄·½H₂O but the conventional representation is CaSO₄·½H₂O. Option A is gypsum, D is anhydrous calcium sulfate. POP is used for making casts, statues, and as a building material.