Question

what happens when a gas is compressed?
volume is increased.
pressure is decreased.
temperature is decreased.
density is increased.

Explanation:

Compressing a gas reduces its volume while the mass of the gas remains constant. Density is defined as $\frac{\text{mass}}{\text{volume}}$. As volume decreases with fixed mass, density rises. The other options are incorrect: compression reduces volume, increases pressure, and typically increases temperature (if no heat loss).

Answer:

Density is increased.