Two waves A and B frequencies $2\;MHz$ and $3MHz$ respectively are beamed in the same direction for communication via sky wave .Which one of there is likely to travel longer distance in the ionosphere before suffering total internal reflection ?

Question

$\begin{array}{1 1} 3\;MHz \\ 5\;MHz \\ both\;3\;MHz \;and \;5\;MHz \\ neither\; of\; the\; two \end{array}$