If over the course of a day, the maximum electron density in the ionosphere varies from 1011 to 1012 m-3; the critical frequency changes approximately from:
A. 2.2 MHz to 7 MHz
B. 2.5 MHz to 8 MHz
C. 2.8 MHz to 9 MHz
D. 3.2 MHz to 10 MHz
Answer: Option C
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