The correct option is (c).
Explanation
The speed of sound in a medium is determined by the medium's properties, specifically its elasticity and density. Generally, sound travels fastest in solids, followed by liquids, and slowest in gases. Within a specific state of matter, factors such as temperature, molecular weight, and salinity influence the speed.
Statement-wise Analysis:
- Statement 1 is Incorrect: According to standard data, at 25°C, the speed of sound in Aluminium is approximately 6420 m/s, whereas in Steel, it is approximately 5960 m/s. Therefore, the speed of sound in Aluminium is higher, not lower, than in Steel.
- Statement 2 is Correct: The speed of sound in a gas is inversely proportional to the square root of its molar mass ($v \propto \frac{1}{\sqrt{M}}$). Since Hydrogen has a much lower molar mass than the gases constituting Air (primarily Nitrogen and Oxygen), sound travels significantly faster in Hydrogen (~1284 m/s) than in Air (~346 m/s).
- Statement 3 is Correct: The presence of salts in seawater increases its density, but it increases the bulk modulus (elasticity) of the water even more significantly. Consequently, sound travels faster in Seawater (~1531 m/s) compared to Distilled water (~1498 m/s).
Key Takeaway:
The speed of sound follows the order: Solids > Liquids > Gases. In solids, Aluminium conducts sound faster than Steel. In gases, lighter gases (like Hydrogen) conduct sound faster than heavier gases (like Air).