What is the modulation index of an over-modulated wave?

Frequencies in the $UHF$ range normally propagate by means of:

When the angle of incidence is $74^{\circ}$,the critical frequency of the $F$ layer is $50 \text{ MHz}$. What is the Maximum Usable Frequency $(MUF)$ in $\text{ MHz}$ (in $.5$)?

The loss of strength of a signal while propagating through a medium is known as

The carrier frequency of a transmitter is provided by a tank circuit of a coil of inductance $49\,\mu H$ and a capacitance of $2.5\,nF$. It is modulated by an audio signal of $12\,kHz$. The frequency range occupied by the side bands is

$A$ bandwidth of $6 \, \text{MHz}$ is available for $A.M.$ transmission. If the maximum audio signal frequency used for modulating the carrier wave is not to exceed $6 \, \text{kHz}$,the number of stations that can be broadcasted within this band simultaneously without interfering with each other will be ..... .