Statement-1 : Electromagnetic waves with frequencies smaller than the critical frequency of ionosphere cannot be used for communications using sky wave propagation.
Statement-2: The refractive index of the ionosphere becomes very high for frequenceis higher than the criritcal frequency.

Options

A. Statement-1 is true: Statement-2 is true, and Statement-2 is correct explanation of Statement-1.
B. Statement-1 is true, Statement-2 is true, but Statement-2 is not a correct explanation of Statement-1.
C. Statement-1 is true, but Statement-2 is false.
D. Statement-1 is false, but Statement-2 is true.

Explanation

If the frequencies of the electromagnetic waves are less than the critical frequency, they will be reflected back by the ionosphere as the refractive index of ionosphere is less than that of free air in the lower part of earth's atmosphere. This is the lower part of earth's atmosphre. This is the basic principle of sky wave propagation. Therefore the statement-1 is false. The statement-2 is true.