The temperature of the air varies

Options

A. Periodically
B. Vertically
C. Horizontally
D. All are correct

Answer

### Step-by-Step Solution:

1. **Understanding Temperature Variation**: The temperature of air does not remain constant; it changes depending on various factors such as the season and altitude.

2. **Seasonal Variation**: In summer, the temperature of the air is generally high due to increased sunlight and longer days. Conversely, in winter, the temperature is low because of shorter days and less sunlight. This shows that air temperature varies periodically with the seasons.

3. **Vertical Variation**: As we move vertically (i.e., as we go higher in altitude), the temperature of the air decreases. This is a common phenomenon observed in the atmosphere where higher altitudes tend to be cooler.

4. **Horizontal Variation**: The temperature of air also varies horizontally. This means that different geographical locations can have different air temperatures. One major reason for this is the angle of incidence of the sun's rays, which changes as you move from the equator towards the poles. The sun's rays strike the equator more directly than they do at the poles, leading to warmer temperatures at the equator and cooler temperatures towards the poles.

5. **Conclusion**: Based on the above points, we can conclude that:
- The temperature of air varies periodically (seasonally).
- The temperature decreases with height (vertically).
- The temperature varies horizontally due to the angle of incidence of sunlight.

6. **Final Answer**: Since all the statements regarding air temperature variation are correct, the correct option is "All are correct".