Explanation:
When light waves enter water from air, several properties of the light waves change. However, the frequency of the light waves remains unchanged.

Wavelength:
The wavelength of a wave is the distance between two consecutive points in the same phase. When light waves enter water from air, the speed of the waves changes because the refractive index of water is different from that of air. According to the equation v = λf, where v is the speed of the wave, λ is the wavelength, and f is the frequency, the wavelength of the light waves will change as the speed changes.

Wavenumber:
The wavenumber of a wave is defined as the number of wavelengths per unit distance. It is the reciprocal of the wavelength. Since the wavelength changes when light waves enter water from air, the wavenumber will also change.

Intensity:
The intensity of a wave is the power transferred per unit area. When light waves enter water from air, some of the light is reflected and refracted. The intensity of the light waves can change as a result of these interactions.

Frequency:
The frequency of a wave is the number of oscillations per unit time. It is a characteristic property of the source of the wave and does not change when the wave enters a different medium. The frequency of the light waves will remain unchanged when they enter water from air.

In conclusion, when light waves enter water from air, the wavelength, wavenumber, and intensity of the waves change, but the frequency remains unchanged.