Sound speed increases with medium density and elasticity

Steps:

• Sound waves propagate via particle vibrations, requiring a medium.
• Speed depends on how quickly particles transfer energy, influenced by density and stiffness (elasticity).
• Compare media: gases have low density/low elasticity; liquids higher density/moderate elasticity; solids highest density/high elasticity.
• Thus, solids enable fastest transmission.

Why D is correct:

• In solids, high elasticity (strong interatomic bonds) and density allow rapid particle collisions, per formula v = √(E/ρ) where E is elastic modulus and ρ is density—solids maximize this ratio.

Why the others are wrong:

• A: Vacuum lacks particles, so sound cannot propagate (speed undefined or zero).
• B: Gases have widely spaced, loosely bound particles, yielding slowest speeds (e.g., ~343 m/s in air).
• C: Liquids offer better conduction than gases but lower elasticity than solids (e.g., ~1480 m/s in water vs. ~5000 m/s in steel).

Final answer: D