Frequencies in the UHF range normally propagate by means of

The correct answer is Option (4) → Space waves

The mode of propagation depends on the frequency. UHF waves (about 300 MHz to 3000 MHz) are far above the range that the ionosphere reflects (up to about 30 MHz), and ground waves lose energy very quickly at such high frequencies.

So UHF signals travel in a straight line from the transmitting antenna to the receiving antenna (line of sight), which is space wave propagation.

Note: The same question was also asked in CUET (UG) 2023 on 09-06-2023 (Slot 3).

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. … At frequencies above 40 MHz, communication is essentially limited to line-of-sight paths.”