Cooling Causes Air Contraction

Steps:

• The cooling unit lowers the temperature of nearby air.
• Lower temperature reduces molecular kinetic energy.
• Molecules slow down and move closer together.
• This contraction increases the air's density.

Why D is correct:

• Cooling decreases molecular motion per the kinetic theory of gases, causing volume contraction and higher density at constant pressure.

Why the others are wrong:

• A: Molecules do not shrink; density decreases contradicts cooling effect.
• B: Molecules do not shrink; first part invalidates despite correct density change.
• C: Molecules move closer, but density decreases is the opposite of contraction.

Final answer: D