Which of the following modulated signals has the best noise tolerance?

If the length of an antenna is $150 \,cm$,the transmission frequency is . . . . . . $MHz$. (Speed of light in vacuum $= 3 \times 10^8 \,ms^{-1}$)

The process of superimposing a message signal on a high-frequency carrier wave is called:

$A$ transmitting and receiving antenna have a height of $d$ meters each. The maximum distance between them for satisfactory communication in Line-of-Sight $(LOS)$ mode is $2d$ kilometers. If the radius of the Earth is $6400 \text{ km}$, then the value of $d$ is: (in $\text{ m}$)

$A$ message signal of peak voltage $12 \ V$ is used to amplitude modulate a carrier signal of frequency $1.2 \ MHz$. The amplitude of the side bands is (in $V$)

The maximum peak-to-peak voltage of an $AM$ wave is $24 \, mV$ and the minimum peak-to-peak voltage is $8 \, mV$. The modulation factor is.....$\%$