Ideal Gas Law Determines Volume Change

Steps:

• Density ρ = m/V; fixed m means ρ increases if V decreases.
• Ideal gas law: PV = nRT; fixed n gives V ∝ T/P.
• To decrease V (increase ρ), increase P and/or decrease T.
• Option C raises P and lowers T, ensuring V shrinks.

Why C is correct:

• Both changes reduce V via V ∝ T/P, guaranteeing higher density per the ideal gas law.

Why the others are wrong:

• A: P decreases and T increases, so V rises and ρ falls.
• B: P decrease may outweigh T decrease, so V could increase and ρ not rise.
• D: T increase may outweigh P increase, so V could expand and ρ not rise.

Final answer: C