Normally, the temperature decreases with the increase in height from the Earth’s surface, because : 1. The atmosphere can be heated upwards only from the Earth’s surface 2. There is more moisture in the upper atmosphere. 3. The air is less dense in the upper atmosphere. Select the correct answer using the codes given below:

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YESPYQ · Accepted Answer

Correct answer: 1 and 3 only. In the troposphere (near earth surface), temperature usually decreases as altitude rises. This is called the lapse rate. On average, the temperature drops by 1°C for every 165 meters of height. This equals about 6.5°C for every kilometer. Statement 1 is correct : The Earth’s surface absorbs solar radi- ation and then re-radiates it as heat. The air in contact with the surface warms up and transfers heat to the layers above through conduction, convection, and radiation. Since the primary heat source is the Earth’s surface, higher altitudes receive less heat, leading to a drop in temperature. Statement 2 is incorrect : Moisture content (water vapor) which accounts for around 1% of air varies greatly in the tropo- sphere, decreases significantly with altitude, as most water vapor is found near the Earth’s surface. The upper atmosphere is drier, not more moist. Statement 3 is correct : As altitude increases, air pressure and density decrease. Less dense air holds less heat, contributing to a decrease in temperature with height. 40

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