Ideal Gas Law: PV = nRT for fixed mass (n constant)

Steps:

• Apply ideal gas law: for fixed n, PV ∝ T.
• At constant volume, P ∝ T, yielding a straight line through origin on P-T graph.
• At constant pressure, V ∝ T, yielding a straight line through origin on V-T graph.
• Identify diagram showing linear relationship starting at T=0 K.

Why A is correct:

• Diagram A shows P or V linearly increasing with T from origin, matching PV = nRT where absolute zero corresponds to zero volume or pressure.

Why the others are wrong:

• B: Nonlinear curve violates direct proportionality in ideal gas law.
• C: Line doesn't pass through origin, ignoring T=0 K behavior.
• D: Decreasing trend contradicts expansion with rising temperature.

Final answer: A