A 'Maritime polar cold unstable' air mass is represented as:

Question

Accepted Answer

The correct answer is Option 1: mPKu. Here's why:

*   **mP:** This signifies "maritime Polar." 'm' indicates that the air mass originates over water (maritime), and 'P' indicates that it originates in a polar region. This aligns with the question's description of a "Maritime polar" air mass.

*   **K:** This signifies that the air mass is colder than the surface over which it is moving. This is important because the question specifies "cold." When a cold air mass moves over a warmer surface, it becomes unstable.

*   **u:** This signifies that the air mass is unstable. This directly corresponds to the "unstable" part of the question's description.

Therefore, 'mPKu' accurately represents a maritime polar air mass that is cold and unstable.

Now, let's explain why the other options are incorrect:

*   **Option 2: mTKu:** 'mT' represents "maritime Tropical." Tropical air masses are warm, not cold, contradicting the question's description. While 'K' still indicates colder than the surface, the fundamental air mass type is wrong.

*   **Option 3: mPWu:** 'mP' is correct for maritime polar, and 'u' is correct for unstable. However, 'W' signifies that the air mass is warmer than the surface over which it is moving. This implies stability, which contradicts the "unstable" part of the question.

*   **Option 4: mTWu:** 'mT' represents "maritime Tropical," which is warm, not cold. 'W' signifies that the air mass is warmer than the surface over which it is moving, implying stability. 'u' signifies unstable, but the initial 'mT' is incorrect, and the 'W' contradicts the overall instability implied by the question.