The speed of sound will be fastest in _____.

Iron bar

The correct answer is option 1. Iron bar.

The speed of sound, which is the rate at which sound waves travel through a medium, depends on the properties of that medium. It is generally faster in denser mediums where the particles are closely packed together, allowing for more efficient transmission of sound waves.

In solids, such as an iron bar, the particles are tightly packed and have strong intermolecular forces. This allows sound waves to propagate quickly through the material, as the particles can quickly transmit the mechanical energy of the wave from one particle to the next. Consequently, the speed of sound in solids is typically higher than in liquids and gases.

In liquids, such as water, the particles are less tightly packed compared to solids but are still closer together than in gases. Sound waves can travel through liquids, but they do so at a slower speed compared to solids due to the looser arrangement of particles and weaker intermolecular forces.

In gases, such as air, the particles are widely spaced apart, and there are weaker intermolecular forces between them. This results in a slower speed of sound compared to solids and liquids. Additionally, in a vacuum (an area devoid of matter), sound waves cannot propagate at all because there are no particles present to transmit the waves.

Therefore, the speed of sound is fastest in solids, followed by liquids, and slowest in gases. This is why the speed of sound would be fastest in an iron bar compared to water, a hilltop, or a vacuum.