Boyle's Law: Pressure inversely proportional to volume at constant temperature

Steps:

• Fixed mass and temperature mean Boyle's Law applies: P ∝ 1/V.
• Initial state: pressure P₁, volume V₁.
• New volume V₂ = 2V₁, temperature unchanged.
• Thus, P₂ V₂ = P₁ V₁, so P₂ = P₁ (V₁ / V₂) = P₁ / 2.

Why A is correct:

• Boyle's Law formula P₁V₁ = P₂V₂ shows pressure halves when volume doubles at constant T.

Why the others are wrong:

• B: Volume change must alter pressure per inverse relationship.
• C: Direct proportionality applies to other laws, not Boyle's.
• D: No basis for tripling; doubling volume yields halving only.

Final answer: A