Final answer:
The humidity would be 50% when the air contains 4 grams of water vapor per cubic meter, as it's half of the maximum 8 grams that defines 100% relative humidity.
Step-by-step explanation:
If one cubic meter of air can hold a maximum of 8 grams of water vapor, this represents 100% relative humidity. When the air contains only 4 grams of water vapor, the relative humidity is half of the maximum. Therefore, to calculate the relative humidity in this situation, we would take the amount of water vapor present (4 grams) and divide it by the maximum amount of water vapor the air can hold at that temperature (8 grams), then multiply by 100 to get a percentage.
Relative humidity = (Water vapor present / Maximum water vapor) x 100
Relative humidity = (4 grams / 8 grams) x 100 = 50%
The humidity in this scenario would be 50% since it is at half the capacity of water vapor that the air can hold at that temperature.