Final answer:
Decreasing the asteroid's mass would make it easier for atmospheric gas particles to escape the asteroid's gravity because it reduces the asteroid's gravitational pull and, hence, the required escape velocity. Decreasing atmospheric temperature can also help, but the effect is not as significant.
Step-by-step explanation:
When considering what makes it easier for atmospheric gas particles to escape an asteroid's gravity, the key concept is the asteroid's escape velocity, which is the speed at which an object must travel to break free of the asteroid's gravitational pull.
Option B) Decreasing the asteroid's mass would decrease its gravitational attraction, thereby reducing the escape velocity required for atmospheric gases to escape. It is not the increase in mass (option A) nor the increasing atmospheric pressure (option D) that would facilitate this, as both would likely enhance the gravitational pull of the asteroid.
Option C) Decreasing atmospheric temperature could also make it easier for gas molecules to escape, as colder gas molecules move slower and are less likely to achieve the escape velocity. However, this effect is not as direct or significant as that of changing the mass of the asteroid.