Frequencies in the UHF range normally propagate by means of:

The correct answer is Option (4) → Space waves

The mode of propagation of a radio signal is decided by its frequency. Ground (surface) waves are absorbed quickly above a few MHz, and the ionosphere reflects sky waves only up to about 30–40 MHz. The UHF band (300 MHz to 3 GHz) lies far above this limit, so UHF signals travel as space waves, in a straight line from the transmitting antenna to the receiving antenna.

Note: The same question was also asked in CUET (UG) 2022 on 06-08-2022 (Slot 2).

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Space Wave – “Another mode of radio wave propagation is by space waves. A space wave travels in a straight line from transmitting antenna to the receiving antenna. Space waves are used for line-of-sight (LOS) communication as well as satellite communication. At frequencies above 40 MHz, communication is essentially limited to line-of-sight paths.”