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

In a line of sight radio communication,a distance of about $50\, km$ is kept between the transmitting and receiving antennas. If the height of the receiving antenna is $70\, m$,then the minimum height of the transmitting antenna should be........$m$ (Radius of the Earth $= 6.4 \times 10^6\, m$)

Match Column $A$ (layers in the ionosphere for skywave propagation) with Column $B$ (their height range).

Column $A$	Column $B$
$A$. $D$-layer	$I$. $250-400 \ km$
$B$. $E$-layer	$II$. $170-190 \ km$
$C$. $F_1$-layer	$III$. $95-120 \ km$
$D$. $F_2$-layer	$IV$. $65-75 \ km$

$A$ baseband signal of $3.5\, MHz$ frequency is modulated with a carrier signal of $3.5\, GHz$ frequency using amplitude modulation. What should be the minimum size of antenna required to transmit the modulated signal?

For the output of an $AM$ detector circuit to follow the envelope of the carrier wave,which condition must be satisfied? ($T_c$ is the time period of the carrier wave.)

$A$ 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 $\text{ V}$)