In which medium among the following does sound travel fastest under normal conditions?

Introduction / Context:
Sound is a mechanical wave that requires a material medium to travel. Its speed depends on the properties of the medium, such as density and elasticity. Generally, sound travels fastest in solids, slower in liquids and slowest in gases. This question asks you to determine in which listed medium sound travels fastest: vacuum, air, glass or water.

Given Data / Assumptions:

• Sound is a longitudinal mechanical wave produced by vibrating sources.
• It requires a material medium such as a gas, liquid or solid to propagate.
• We consider typical conditions near room temperature and atmospheric pressure.
• The media to compare are vacuum, air, water and glass.

Concept / Approach:
In a vacuum, there are no particles, so sound cannot travel at all; its speed is effectively zero. In gases like air, particles are far apart and interactions are weaker, so sound speed is relatively low (around 340 m/s at room temperature). In liquids like water, particles are closer together and interactions are stronger, so sound travels faster (around 1500 m/s). In solids such as glass or steel, particles are very tightly packed and strongly bonded, allowing sound to travel fastest (often several thousand metres per second). Therefore, among the given options, glass, being a solid, provides the highest speed of sound.

Step-by-Step Solution:
Step 1: Recognise that sound cannot travel in a vacuum because there are no particles to transmit the vibrations. Step 2: Recall that in air (a gas), the speed of sound is relatively low compared with liquids and solids. Step 3: Recall that in water (a liquid), sound travels faster than in air due to closer particle spacing and stronger interactions. Step 4: Recognise that in solids like glass, particles are most tightly packed and forces between them are strongest, generally giving the highest sound speed. Step 5: Therefore, among vacuum, air, glass and water, sound travels fastest in glass.

Verification / Alternative check:
Approximate values support this reasoning: in dry air at room temperature, sound travels at about 340 m/s; in water, around 1500 m/s; in glass or steel, several thousand metres per second, often in the range of 4000–6000 m/s. The speed in a vacuum for sound is effectively zero, since mechanical waves cannot propagate without matter. Physics textbooks and exam questions consistently emphasise the rule: sound travels fastest in solids, slower in liquids and slowest in gases.

Why Other Options Are Wrong:
Vacuum: Sound cannot travel in a vacuum at all because there are no particles to carry the disturbance.

Air: While sound does travel in air, its speed is lower than in water and much lower than in solids like glass.
Water: Sound travels faster in water than in air, but not as fast as in most solids such as glass.

Common Pitfalls:
Some learners mistakenly assume that because light travels fastest in a vacuum, sound might also, but sound and light are different kinds of waves. Light is an electromagnetic wave that does not require a medium, while sound is mechanical and must have particles to propagate. Another confusion is between density and speed; it is not just density but the combination of density and elasticity that determines sound speed, leading to the general trend of fastest in solids.

Final Answer:
Among the given options, sound travels fastest in Glass.