The electron density of $E, F_1, F_2$ layers of the ionosphere is $2 \times 10^{11} \, m^{-3}$,$5 \times 10^{11} \, m^{-3}$,and $8 \times 10^{11} \, m^{-3}$ respectively. What is the ratio of critical frequencies for the reflection of radio waves?

  • A
    $2 : 4 : 3$
  • B
    $4 : 3 : 2$
  • C
    $2 : 3 : 4$
  • D
    $3 : 2 : 4$

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