MCQ Detailed View

The ionosphere is a region of Earth’s upper atmosphere that extends roughly from 60 km to 1,000 km above the surface. It is characterized by the presence of ions and free electrons, which are created when solar ultraviolet (UV) radiation and X-rays ionize atmospheric gases such as oxygen and nitrogen.

The key feature of the ionosphere is that its density of charged particles changes with the day-night cycle. During the daytime, sunlight is continuously ionizing atmospheric gases, which leads to a high concentration of ions and electrons. This makes the ionosphere denser and more effective at reflecting and refracting radio waves, which is why long-distance radio communication is more reliable in the daytime.

At night, when the Sun is no longer shining on that part of the Earth, ionization drops significantly. Many of the free electrons recombine with positive ions, reducing the overall density of charged particles. As a result, the ionosphere becomes less dense at night compared to the daytime. However, certain higher layers like the F-region remain ionized longer, allowing some radio communication to continue.

Comparing the options:

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  Option A is incorrect because density does not decrease both morning and night; it peaks in the day.

  
  


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  Option B is correct: ion density is high in the daytime and decreases at night.

  
  


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  Option C is misleading, as density does not increase at night.

  
  


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  Option D is incorrect since one option is clearly true.

  
  

Therefore, the correct statement about the ionosphere is: High density in daytime, decreases at night.