Sky wave propagation is not possible for frequencies

Given below are two statements
Statement $I:$ For transmitting a signal,the size of the antenna $(l)$ should be comparable to the wavelength of the signal (at least $l = \frac{\lambda}{4}$ in dimension).
Statement $II:$ In amplitude modulation,the amplitude of the carrier wave remains constant (unchanged).
In the light of the above statements,choose the most appropriate answer from the options given below.

$A$ $TV$ transmitter has a range of $50 \ km$. The height of the $TV$ transmitter is $......$ (Radius of the earth $R_e = 6.4 \times 10^6 \ m$) (in $m$)

The bandwidth of a coaxial cable is approximately ........ .

In $TV$ transmission,the audio signal is ........ modulated and the video signal is ........ modulated.

For an amplitude modulated wave,the maximum and minimum amplitudes are $12 \,V$ and $3 \,V$ respectively. Then the modulation index is