In meteorology, air is said to be saturated when which of the following conditions is reached?

Introduction / Context:
The concepts of humidity and saturation are important in weather forecasting, cloud formation, and the study of climate. When air cannot hold any more water vapour at a given temperature and pressure, it is described as saturated. This condition is closely associated with dew point, condensation, and the formation of fog or clouds. This question asks you to identify the correct definition of saturated air among several options.

Given Data / Assumptions:

• We are dealing with atmospheric air that contains varying amounts of water vapour.
• Temperature plays a major role in how much water vapour air can hold.
• Options suggest pressure, maximum water vapour content, air thickness, and barren land as possible conditions.
• We assume standard meteorological definitions of saturation and humidity.

Concept / Approach:
At a given temperature, there is a maximum partial pressure of water vapour that air can sustain in equilibrium with liquid water. When this limit is reached, the air is saturated and relative humidity is 100 percent. Any further cooling or addition of water vapour will lead to condensation. Saturation is not defined by minimum total air pressure, thickness of the air column, or the type of land over which the air is moving. It is specifically about the maximum content of water vapour the air can hold at that temperature and pressure.

Step-by-Step Solution:
Step 1: Recall that warm air can hold more water vapour than cold air; the saturation level depends strongly on temperature. Step 2: Understand that saturation occurs when the rate of water molecules entering the air from evaporation equals the rate condensing back to liquid, establishing equilibrium. Step 3: At this equilibrium, the air contains the maximum possible water vapour for that temperature, and relative humidity becomes 100 percent. Step 4: Recognise that total air pressure and the nature of the surface (barren or vegetated) can influence humidity but do not define saturation. Step 5: Conclude that air is said to be saturated when it contains the maximum possible amount of water vapour at the prevailing temperature.

Verification / Alternative check:
Weather reports often mention dew point, which is the temperature to which air must be cooled for saturation to occur. At dew point, air can no longer hold additional water vapour and condensation begins, forming dew, fog, or clouds. Relative humidity is defined as the ratio of current water vapour content to the maximum possible at that temperature, expressed as a percentage. When this ratio reaches 100 percent, the air is saturated. These standard definitions confirm that saturation refers to maximum water vapour content, not to minimum pressure or other unrelated factors.

Why Other Options Are Wrong:
Its pressure is at the minimum possible value: Air pressure can be low or high regardless of saturation; saturation concerns water vapour content, not total pressure alone. Its thickness above the ground is at a maximum: The vertical thickness of the atmosphere is not how meteorologists define saturation. It is blowing over completely barren land: While surface conditions affect evaporation rates, they do not by themselves determine whether air is saturated.

Common Pitfalls:
Learners may confuse saturation with high humidity in general, thinking that air is saturated whenever it feels very humid. In reality, saturation is a precise condition where relative humidity reaches 100 percent. Another confusion is between total air pressure and water vapour pressure; only the latter directly relates to saturation. Remember that saturation means the air is holding as much water vapour as it can at that temperature, and any further cooling will cause condensation.

Final Answer:
Air is said to be saturated when it contains the maximum possible amount of water vapour at that temperature.