Final answer:
The relative humidity is calculated as the ratio of the current water vapor amount to the maximum water vapor possible at that temperature, multiplied by 100%. With the given values, the relative humidity is 50%.
Step-by-step explanation:
The question asks to calculate the relative humidity, which is the ratio of the current amount of water vapor in the air to the maximum amount of water vapor the air can hold at that temperature. Given the air temperature is 40 degrees Celsius, the maximum water vapor the air can hold at this temperature is 50 grams per cubic meter, and it is currently holding 25 grams of water vapor per cubic meter, the relative humidity can be calculated as follows:
Relative humidity = (Current water vapor amount / Maximum water vapor amount) × 100%
Relative humidity = (25 g/m³ / 50 g/m³) × 100% = 50%
Therefore, the correct answer is A) 50%.