Which equation expresses the ideal gas law when temperature and amount are constant, with the correct option placed last?

• A. PV = nRT
• B. P = nRT / V
• C. V = nRT / P
• D. PV = nRT

Answer: (D)

PV = nRT expresses how pressure and volume relate for an ideal gas. If temperature and the amount of gas are fixed, then n and T are constants, so the product nRT stays the same. That makes the product PV a constant as well, meaning pressure and volume are inversely related: as volume goes up, pressure goes down, keeping PV constant. The last choice states PV = nRT directly, which is the clearest way to capture this relationship under those fixed conditions. The other forms are algebraic rearrangements (P = nRT/V or V = nRT/P) of the same idea, describing the same inverse relation when n and T don’t change, but the product form is the direct expression.