In short wave communication, waves of which of the following...

We know that the artificial frequency of a sky wave for reflection from an ionospheric layer of the atmosphere is given by, $v_c=9 N^{1 / 2}$ where $n$ is the number density of electrons $/ \mathrm{m}^3$. It is given that $N=10^{11} / \mathrm{m}^3$ \therefore \quad v_c=9 \times\left(10^{11}\right)^{1 / 2}=2.8 $\times$10^6 $\mathrm{~Hz}=$2.8 $\mathrm{MHz} \text{. }$Hence the wave of frequency $2 \mathrm{MHz}$ will be reflected back.