The signal obtained at the output of a microphone is of which type?

$A$ carrier wave of peak voltage $16 \text{ V}$ is used to transmit a signal. If the modulation index is $75 \%$, the peak voltage of the modulating signal is (in $\text{ V}$)

If the amplitude of the modulated wave and the amplitude of the signal are equal, then the modulation index is .....$\%$

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.

An antenna behaves as a resonant circuit only when its length is

$A$ telephonic communication service is working at a carrier frequency of $10 \ GHz$. Only $10\%$ of it is utilized for transmission. How many telephonic channels can be transmitted simultaneously if each channel requires a bandwidth of $5 \ kHz$?