Positive catalysts work by: MCQ with Answer and Explanation

Explanation:
Plaster of Paris (CaSO₄·½H₂O) is formed by heating gypsum (CaSO₄·2H₂O) at 373 K (100°C). This causes it to lose 1.5 molecules of water per formula unit. If heated significantly above 473 K, it loses all water and forms dead burnt plaster (anhydrous CaSO₄), which cannot set with water.

Explanation:
Graphite mixed with clay forms pencil 'lead'. Its layered structure marks paper. Diamond is used in cutting, fullerene in nanotechnology, charcoal in filters and fuel.

Explanation:
Boyle's law: P₁V₁ = P₂V₂. Given P₁=1.0 atm, V₁=2.0 L, P₂=4.0 atm. V₂ = (1.0 × 2.0) / 4.0 = 0.5 L. Volume decreases as pressure increases, because gas is compressible. The product PV is constant for a fixed mass of gas at constant T. Scuba divers experience this; as they dive deeper, pressure increases, reducing air volume in lungs.