The speed of sound travelling in various media increases in the order:

Analyze the question

You are asked to arrange the media (air, water, iron) in order of increasing speed of sound, from slowest to fastest.

Concept

Sound travels by passing vibrations from particle to particle. The closer and more tightly bound the particles are, and the more elastic the medium, the faster sound travels. So in general:

speed in solids > speed in liquids > speed in gases

Typical values

• Air (about 20 °C): ≈ 340 m/s
• Water: ≈ 1,500 m/s
• Iron/steel: ≈ 5,000 m/s

Solution

1. Air is a gas, with widely spaced particles, so it has the slowest speed.
2. Water is a liquid, with particles closer together, so it is faster than air.
3. Iron is a solid, with particles tightly packed and strongly bound, so it has the fastest speed.

Increasing order: air → water → iron bar

Checking the options

• A. air, iron bar, water: wrong, because iron is faster than water.
• B. air, water, iron bar: correct.
• C. iron, bar water, air: this is a garbled option and reverses the order.
• D. water, air, iron bar: wrong, because air is slower than water.
• E. water, iron bar, air: wrong, because air is the slowest.

Exam tip

Remember "Sound Loves Solids": the speed goes S > L > G (Solid, Liquid, Gas). For "increasing" order, reverse it: Gas → Liquid → Solid. Always check whether the question says increasing or decreasing, because examiners often use this to trap students.