Which one of the following layers of the atmosphere is responsible for the deflection of radio waves ?

Correct answer: Ionosphere (4). The ionosphere is a region of the upper atmosphere populated by ions and free electrons produced by solar radiation; these charged particles give the layer strong refractive and reflective properties for radio waves [2]. Radio waves transmitted from Earth can be reflected back to the surface by the ionosphere, enabling long-distance (skywave) communication beyond the horizon [1]. Ionospheric refraction and reflection are frequency-dependent: frequencies below the critical frequency are reflected while higher frequencies penetrate or are absorbed, which governs which bands can use skywave propagation [3]. Other atmospheric layers (troposphere, stratosphere, mesosphere) lack the ionization needed to produce such consistent radio-wave reflection.

Sources

1. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Structure of the Atmosphere > p. 8
2. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > STRUCTURE OF THE ATMOSPHERE > p. 65
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Why Are Microwaves And Some Radio Waves Not Reflected By The Ionosphere? > p. 278