The critical frequency for sky wave propagation if maximum number density of electrons in ionosphere is ${10}^{10} {\mathrm{m}}^{-3}$ is,

Frequencies higher than $5 \mathrm{MHz}$ are found not to be reflected by the ionosphere on a particular day at a place. The maximum electron density of the ionosphere is,

A TV tower has height $150 \mathrm{m}$. By how much should the height of tower be increased to double its coverage range?

How much time is taken by an information to pass from one place to another at a distance of $60 \mathrm{km}$ in space communication?

Amplitude modulation is useful for broadcasting in communication systems because,

Assertion: Communication in UHF/VHF regions can be established by space wave or tropospheric wave.

Reason: Communication in UHF/VHF regions is not limited to line of sight distance but can be achieved for very large distances.

In satellite communication,
(i) the frequency used lies between $6 \mathrm{MHz}$ and $10 \mathrm{MHz}$,
(ii) the uplink and downlink frequencies are different,
(iii) the orbit of geostationary satellite lies in the equatorial plane at an inclination of $0°$.
In the above statements,

Assertion: A dish antenna is highly directional.

Reason: A dipole antenna is unidirectional.

Assertion: Modulation index is the degree to which the carrier wave is modulated.

Reason: For strong and clear reception, the value of modulation index should be very small.