Which of the following options is $NOT$ correct? We need modulation for:

In amplitude modulation of waves,the maximum amplitude is $30 \text{ mV}$ and minimum amplitude is $5 \text{ mV}$,then the modulation index is

In an amplitude modulation,a modulating signal having amplitude of $X$ Volt is superimposed with a carrier signal of amplitude $Y$ Volt in the first case. In the second case,the same modulating signal is superimposed with a different carrier signal of amplitude $2Y$ Volt. The ratio of the modulation index in the two cases respectively will be:

In $AM$ transmission,the bandwidth of transmission is $10 \, kHz$ and the carrier frequency is $100 \, kHz$. Then,the sideband frequencies are given by:

For an amplitude-modulated wave, the audio frequency is $500 \, \text{cycles/second}$. What is the actual carrier frequency in $\text{cycles/sec}$?

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	$IV$. $65-75 \ km$