If temperature rises in the afternoon and water vapour remains nearly the same how will afternoon relative humidity compare with morning?

Correct answer: Lower

Correct answer: C, lower. Relative humidity is the ratio of the water vapour actually present to the maximum water vapour the air could hold at its current temperature, expressed as a percentage. When temperature rises, the saturation vapour pressure and the moisture-holding capacity of air increase. If the actual water-vapour content remains nearly unchanged, the numerator stays almost the same while the saturation value in the denominator becomes larger. The ratio therefore decreases. This is why relative humidity often falls during the warmer part of the day, even without a large loss of water vapour. A is incorrect because warming normally lowers, not raises, relative humidity under the stated condition. B is incorrect because 100% occurs only when actual vapour pressure equals saturation vapour pressure. D is incorrect because relative humidity is not negative; it ranges from near 0% to 100% in ordinary conditions. The word “nearly” allows a practical comparison, while the controlling idea is warming with almost unchanged moisture. Memory cue: warmer air can hold more vapour, so unchanged moisture gives lower relative humidity.