Statement I : Sound wave cannot propagate in vaccum. Statement I : Sound waves are elastic waves and require a medium to propagate

Statement I is true because sound waves are mechanical waves that require a physical medium to propagate; since a vacuum lacks any medium, sound cannot travel through it [3]. Statement II is also true and provides the correct explanation. Sound waves are classified as elastic waves because their propagation depends on the elastic restoring forces of the medium. When particles in a solid, liquid, or gas are displaced, these elastic forces, combined with the inertia of the material, create the oscillatory vibrations (compressions and rarefactions) that constitute the sound wave [1]. Because sound relies on the 'stretching and squeezing' of a material's density to transmit energy, the absence of an elastic medium in a vacuum fundamentally prevents sound propagation [2]. Thus, the elastic nature of sound waves is the reason they cannot exist in a vacuum.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 5: Earths Magnetic Field (Geomagnetic Field) > Why Do Sound Waves Travel Faster In A Denser Medium Whereas Light Travels Slower? > p. 64
2. [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > Propagation of Earthquake Waves > p. 20
3. [2] https://www.sciencedirect.com/topics/physics-and-astronomy/sound-wave