Coal rank increases with burial depth, temperature, and pressure (coalification). The correct sequence from lowest to highest rank is: Peat → Lignite → Sub-bituminous → Bituminous → Anthracite. With increasing rank: moisture decreases, carbon content increases, calorific value increases (up to anthracite), and volatile matter decreases. Vitrinite reflectance (%Ro) quantifies rank: Peat <0.2%, Lignite 0.2–0.4%, Bituminous 0.5–2.0%, Anthracite >2.0%.