When lightwaves pass from air to glass, the variables affected are

When light passes from air into glass its propagation speed changes because glass has a higher optical density; refraction is a consequence of this change in speed [2]. Electromagnetic boundary conditions at the interface enforce continuity of the oscillating fields, which requires the temporal frequency of the light to remain the same across the boundary. Since v = f·λ and f is unchanged, a reduced speed in glass forces a proportionate decrease in wavelength inside the glass [3]. Therefore the variables affected are the velocity (speed) and the wavelength of the light — option 4.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > Activity 9.10 > p. 147
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.2 The Refractive Index > p. 148
3. [3] https://www.ck12.org/flexi/physical-science/wave-speed/when-light-passes-from-air-into-another-medium-such-as-glass-its-wavelength-and-speed-change-but-its-frequency-remains-the-same-for-example-when-light-of-wavelength-550-nm-and-frequency-5-45-x-1014-hz-passes-from-air-into-thin-gla/