Which of the following best describes the behavior of gases under increased pressure?

The behavior of gases under increased pressure is best characterized by compression into a smaller volume. This relationship is described by Boyle's Law, which states that at constant temperature, the volume of a given mass of gas is inversely proportional to the pressure applied to it. As pressure increases, the gas molecules are forced closer together, resulting in a decrease in volume.

In practical terms, if you take a gas inside a sealed container and your surroundings apply more pressure (for instance, by decreasing the volume of the container), the gas will experience a decrease in its volume as its molecules are compressed due to the increased pressure.

This concept is foundational to understanding how gases behave in various conditions, and it's fundamental in various applications, such as in gas storage and the functioning of syringes or internal combustion engines.