Explain the factors that affect the speed of sound in a gas. Why is sound fastest in solids?

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Open. The speed of sound depends on the medium: solids > liquids > gases.
2 · Density. v ∝ 1/√ρ: the denser the gas, the slower the sound.
3 · Temperature. Speed rises with temperature: vT = v₀ + 0.61 T, about 0.61 m/s for each °C.
4 · Humidity. Humid air is less dense, so sound travels faster in it.
5 · Real-life link. Count the seconds between lightning and thunder: distance ≈ 340 m × number of seconds.
6 · Close. Pressure has no effect at constant temperature; solids are fastest because their particles are close and elastic.

Scoring tip: Give the rule (the ∝ relation or the 0.61 m/s figure) with each factor, not just 'increases' or 'decreases'.