Iron
Explanation
Sound is a longitudinal mechanical wave that requires a material medium for propagation. The speed at which sound travels through a medium depends primarily on the medium's elasticity (stiffness) and density. The general relationship is that sound travels faster in media with higher elasticity.
Analysis of Media Types:
- Solids (Iron): In solids, atoms are tightly packed and held together by strong inter-molecular forces, giving them high elasticity. Consequently, mechanical disturbances (sound waves) are transmitted most rapidly. The speed of sound in iron is approximately 5,950 m/s.
- Liquids (Water, Ethanol): Liquids are less elastic than solids but more elastic than gases. The speed of sound in water is approximately 1,480 m/s, while in ethanol it is roughly 1,160 m/s.
- Gases (Air): Gases have the lowest elasticity among the three states of matter. Therefore, sound travels slowest in gases. The speed of sound in air is approximately 343 m/s at 20°C.
Conclusion:
Comparing the given options, Iron is a solid, Water and Ethanol are liquids, and Air is a gas. Therefore, sound travels fastest in Iron.
Key Takeaway:
The speed of sound generally follows the order: Solids > Liquids > Gases. This is because the effect of higher elasticity in solids dominates over the effect of density, facilitating faster wave propagation.