Mass conservation in closed system

Steps:

• Gas is trapped in a cylinder, forming a closed system with no exchange of matter.
• Compression by piston reduces volume but does not add or remove gas particles.
• At constant temperature, only volume and pressure adjust per gas laws.
• Mass, as total matter, remains invariant in this isolated process.

Why B is correct:

• Mass is conserved in a closed system, as defined by the law of conservation of mass—no atoms are created or destroyed.

Why the others are wrong:

• A: Density increases because mass stays constant while volume decreases (density = mass/volume).
• C: Pressure increases per Boyle's law (PV = constant at fixed T) as volume shrinks.
• D: Volume decreases directly due to piston compression.

Final answer: B