Which statement is true about humidity?

Question

Options

• AIf the relative humidity is zero, there is no water vapor present.
• BAs the air temperature decreases, its ability to hold water increases.
• CIf the relative humidity is 50%, the air is holding all the water vapor it can.
• DThe amount of water that can be contained in the room air is fixed regardless of the room temperature.

• A
  76% (47)
• B
  3% (2)
• C
  13% (8)
• D
  8% (5)

Explanation

Relative humidity is a ratio: the amount of water vapor actually in the air divided by the maximum amount the air could hold at that temperature. If that ratio is zero, the numerator must be zero, meaning there is literally no water vapor present - making A correct.

Option B is the opposite of the truth: as temperature decreases, air's capacity to hold water vapor decreases, which is why cold air feels dry and why dew forms as surfaces cool. Option C confuses 50% with 100% - at 50% relative humidity, the air is only half saturated and can still absorb significantly more moisture. Option D is also false; the maximum water vapor capacity of air rises with temperature, which is why humid summer heat feels so oppressive compared to humid winter cold.

Memory tip: Think of relative humidity like a progress bar - 0% means the bar is completely empty (no water vapor at all), and the total length of the bar itself stretches longer as temperature rises.

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