The correct option is (c).
Explanation
Sound waves are longitudinal mechanical waves that propagate through a medium via a series of compressions (regions of high pressure) and rarefactions (regions of low pressure). The fundamental characteristics of these waves include wavelength, frequency, time period, and amplitude.
Statement-wise Analysis:
- Statement 1 is Correct: The wavelength ($\lambda$) is defined as the distance between two consecutive compressions or two consecutive rarefactions. It represents the spatial length of one complete wave cycle.
- Statement 2 is Incorrect: The time taken for one complete oscillation in the density of the medium is called the Time Period ($T$). Frequency ($\nu$ or $f$) is defined as the number of complete oscillations per unit time. The relationship between the two is inverse: $f = \frac{1}{T}$.
- Statement 3 is Correct: The SI unit of frequency is the Hertz (Hz), named after Heinrich Hertz. One Hertz is equivalent to one oscillation per second ($s^{-1}$).
Key Takeaway:
It is crucial to distinguish between Time Period (the duration of one cycle) and Frequency (the rate of cycles per second). Wavelength measures the spatial distance between identical points on consecutive waves.