The normal lapse rate of temperature per kilometer is:

Correct option is C

The correct answer is (c) 6.4°C. The normal lapse rate of temperature is the average rate at which temperature decreases with an increase in altitude in the troposphere. The temperature typically decreases by 6.4°C per kilometer (or 3.5°F per 1,000 feet) as you ascend in the atmosphere.
(B) Explanation:
· The normal lapse rate applies to the troposphere, the lowest layer of Earth's atmosphere where weather events occur.
· The lapse rate indicates how air temperature decreases with increasing altitude under normal atmospheric conditions.
· At an average rate of 6.4°C per kilometer, temperature decreases steadily as altitude increases.
(C) Types of Lapse Rates:
1. Normal (Environmental) Lapse Rate:
· Average rate of temperature decrease: 6.4°C per kilometer.
2. Dry Adiabatic Lapse Rate (DALR):
· For dry air, temperature decreases by 10°C per kilometer due to rising and expanding air.
3. Moist Adiabatic Lapse Rate (MALR):
· For saturated air, temperature decreases by approximately 5°C to 7°C per kilometer, depending on moisture content.
4. Inversion:
· A condition where temperature increases with altitude, disrupting the normal lapse rate.
(D) Additional Knowledge:
· (a) 9.6°C:
· Incorrect. This rate is higher than the typical dry adiabatic lapse rate.
· (b) 10.6°C:
· Incorrect. This is not a standard lapse rate; the dry adiabatic lapse rate is 10°C per kilometer.
· (c) 6.4°C:
· Correct. Represents the average environmental lapse rate in the troposphere.
· (d) 4.6°C:
· Incorrect. This rate is lower than the average moist adiabatic lapse rate.
(E) Key Points:
1. The normal lapse rate is 6.4°C per kilometer in the troposphere.
2. Temperature typically decreases with altitude under normal conditions.
3. The lapse rate influences weather patterns and cloud formation.
4. Different lapse rates (dry and moist) depend on humidity and atmospheric conditions.
5. Temperature inversions can lead to pollution trapping near the surface.