question_answer

In earth's atmosphere, for \[{{F}_{2}}\] -layer, the virtual height and critical frequency in night time are

A)  \[210\,km\] and \[5\text{ }MHz\]

B)        \[250\,km\] and \[6\,MHz\]

C) \[280\text{ }km\] and \[7\text{ }MHz\]

D) \[350\,km\] and \[6\,MHz\]