Which wave is used for satellite communication?
(A) Space wave
(B) Sky wave
(C) Ground wave
(D) Microwave

Hint:There are many types of waves used for communication of signals. Without the use of waves long distance transfer of signals and communication is not possible.Microwave, sky wave, infrared radiation, radio waves etc are the types of wave communication.

Complete step by step answer:
Now let us first see what space wave is- The space wave is a type of radio wave propagation. These types of propagation are used for communication within $20\,km$ radius of the earth’s atmosphere. These signals are sent directly from the transmitter to the receiver through the line of sight. By using space waves to transmit messages to the earth’s antennas satellites communicate. These signals are then collected by the antennas and information originating from those signals is analyzed.
Sky wave- Sky wave is also a type of radio wave propagation. These are used for longer distances than space waves for propagation. The wave that spreads through the atmosphere and is reflected back by the earth’s atmosphere ionosphere is called sky wave propagation. These signals are also sent directly from the transmitter to the receiver through the line of sight.
Ground wave- Another method of propagation is the ground wave. Land wave propagation is a radio wave propagation process that uses the region for transmitting between the earth’s surface and the ionosphere. Microwave- Microwave wave signals typically travel in almost straight lines from transmitter to receiver. Flat surfaces are representative of microwave signals. To bounce a microwave signal across a hill or a building that would otherwise obstruct its direction, plane reflectors can be used.From the above observations it can be concluded that the space wave is used for satellite communication.
Hence, option A is correct.

Note:The space wave, sky wave and ground wave are types of radio communication. The space and sky wave may appear to be similar since both are types of radio wave propagation but only space wave propagation is used for satellite communication as space waves transmit signals to the troposphere.