In coal mining, what happens to gas volume when barometric pressure falls and temperature rises?

When the temperature rises, the gas molecules gain energy and move more rapidly, leading to an increase in gas volume according to Charles's Law, which states that for a given amount of gas at constant pressure, the volume of the gas is directly proportional to its temperature.

Additionally, when barometric pressure falls, the external pressure on the gas decreases. According to Boyle's Law, if the temperature is kept constant, a decrease in pressure will cause the volume of a gas to expand — meaning that the gas will take up more space.

In the scenario where the temperature rises and the barometric pressure falls simultaneously, both factors contribute to an increase in gas volume. The increased kinetic energy from the higher temperature causes the gas to expand, while the lower pressure allows for greater expansion.

Therefore, the correct choice reflects the combined effects of rising temperature and falling pressure, resulting in the gas expanding in volume.