A diagram that shows which phase of a substance is most stable at various temperatures and pressures is called

• A. Phase Diagram
• B. Osmotic Pressure
• C. Equilibrium
• D. Solubility Product Constant

Answer: (A)

This diagram maps which phase is stable for a substance over different temperatures and pressures. At any given temperature and pressure, the phase with the lowest Gibbs free energy is the stable one, so the diagram shows regions where solid, liquid, or gas exist as the favored form. The lines on the diagram are phase boundaries where two phases are in equilibrium with each other (solid–liquid, liquid–gas, solid–gas). Points like the triple point indicate conditions where all three phases coexist, and the critical point marks where liquid and gas become indistinguishable. This tool helps predict whether a material will be solid, liquid, or gas under specific conditions. The other terms don’t describe a map of phase stability: osmotic pressure relates to solutions, equilibrium is a general balance concept, and the solubility product constant concerns solubility, not phase stability by temperature and pressure.