Which term describes the boundary between two different air masses?

• A. Front
• B. Air Mass
• C. Lapse Rate
• D. Tropopause

Answer: (A)

A front is the boundary that forms where two contrasting air masses meet. When two large bodies of air with different temperatures, humidity, and densities come into contact, a distinct surface—called a front—develops where their properties shift abruptly. This boundary is where you typically see the most noticeable weather changes, such as shifts in wind, temperature, and cloud/precipitation patterns, because air is forced to rise or interact as the contrasting masses meet. The other terms describe different concepts: an air mass is the large body of air itself, the lapse rate is how temperature changes with height, and the tropopause is the boundary between the troposphere and the stratosphere.