__ 2. Why do Mercur and our Moon lack an atmosphere? A planet's . ability to retain an atmosphere depends on __ More massine planets retain their atmospheres because __ need a higher speed to escape . This is known as the __ mass and molecule:atoms mass and temperature and temperature escape inertia atoms and molecules, escape velocity b temperature , molecules. escape velocity c. mass; atoms escape velocity atoms and molecules.mass and temperature ; escape inertia

The answer is **c. mass; atoms; escape velocity**.<br /><br />Here's why:<br /><br />* **Mass:** A planet's mass directly affects its gravitational pull. More massive planets have stronger gravity. This stronger gravity is better at holding onto atmospheric gases.<br /><br />* **Atoms and molecules:** Atmospheres are made up of atoms and molecules. These particles are constantly moving.<br /><br />* **Escape velocity:** This is the minimum speed a particle needs to overcome a planet's gravitational pull and escape into space. If a planet has a low escape velocity, lighter atmospheric gases like hydrogen and helium can easily reach this speed and escape.<br /><br />Mercury and the Moon lack substantial atmospheres because they have relatively low masses, resulting in weak gravitational pulls and low escape velocities. The atoms and molecules in any potential atmosphere they might have had were able to reach escape velocity due to their thermal energy (related to temperature) and escape into space.<br />