Gases have two types of specific heats. What are they?

Gases are unique in that they have two distinct specific heats, unlike solids and liquids which have only one. Option A (Cv and Cp) is CORRECT — gases have two specific heats: (1) Specific heat at constant volume (Cv) — the heat required to raise the temperature of 1 mole of gas by 1°C while keeping the volume constant. (2) Specific heat at constant pressure (Cp) — the heat required to raise the temperature of 1 mole of gas by 1°C while keeping the pressure constant. At constant pressure, the gas expands and does work against external pressure, so more heat is needed. The ratio γ = Cp/Cv is called the adiabatic index or heat capacity ratio and is approximately 1.4 for diatomic gases like air (N₂, O₂). Option B (Cs and Ck) is incorrect — these are not standard symbols for specific heats of gases in thermodynamics. Option C (Cf and Cb) is incorrect — no such standard thermodynamic quantities exist. Option D (Ch and Cl) is incorrect — these have no standard meaning in thermodynamics related to specific heats of gases.