Range of frequencies allotted for commercial FM radio broadcast is

A sky wave with a frequency $55 \mathrm{MHz}$ is incident on $D$-region of earth's atmosphere at $45°$. The angle of refraction is (electron density for $D$-region is $400 \mathrm{electrons} {\mathrm{cm}}^{-3}$ ),

An oscillator is producing FM waves of frequency $2 \,\mathrm{kHz}$ with a variation of $10\, \mathrm{kHz}$. What is the modulating index? 

Broadcasting antennas are generally

The attenuation in optical fibre is mainly due to,