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

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having an electron density of $10^{11} \text{ per } m^3$ (in $\text{ MHz}$)?

If $E_c$ and $E_m$ are peak values of carrier and modulating signals,respectively,then for $100 \%$ modulation,

Which of the following statements is $NOT$ true?

The waves which are reflected back to the earth by the ionosphere are:

Data exchange between two computers occurs through which type of signal?