For radio and television broadcasting,what type of signals are used to carry information?

This question has Statement-$1$ and Statement-$2$. Of the four choices given after the statements, choose the one that best describes the two statements.
Statement-$1$: Sky wave signals are used for long-distance radio communication. These signals are, in general, less stable than ground wave signals.
Statement-$2$: The state of the ionosphere varies from hour to hour, day to day, and season to season.

The maximum frequency of transmitted radio waves above which the radio waves are no longer reflected back by the ionosphere is . . . . . . ($N=$ maximum electron density of the ionosphere, $g=$ acceleration due to gravity).

The maximum usable frequency $(MUF)$ in the $F$-region layer is $x$,when the critical frequency is $60 \, MHz$ and the angle of incidence is $70^\circ$. Then $x$ is ....... $MHz$.

In amplitude modulation,the amplitude of the carrier wave is $10 \ V$ and the amplitude of one of the sidebands is $2 \ V$. Then the modulation index is

Space wave propagation is possible for which frequency range?