Which condition leads to the most stable air mass?

The condition that leads to the most stable air mass is associated with cool, dry conditions. In meteorology, stability in an air mass means that it resists vertical motion; that is, parcels of air do not rise easily through the surrounding air. Cool, dry air is denser than warm, moist air, which tends to cause a stable environment. This stability prevents turbulence and vertical mixing, resulting in clearer skies and calm weather as opposed to conditions with significant atmospheric movement.

When the air mass is cool and dry, the likelihood of instant lift or turbulence decreases. Cool air is relatively heavy, and it will not readily rise unless it is forced to do so, which contributes to overall stability. This is in contrast to warm and moist conditions that frequently lead to convection and can trigger the development of thunderstorms or other weather phenomena.

In summary, cool, dry air promotes stability, making it less prone to vertical movement, thus leading to a more stable air mass than other options.