The speed of light will be minimum while passing through

The speed of light in a medium is inversely related to that medium’s refractive index: n = c/v, so a larger refractive index means a smaller speed v. Table values show vacuum (n≈1.000), air (n≈1.0003), water (n≈1.33) and typical glass (n≈1.5 or higher), indicating glass has a higher refractive index than water or air [1]. Textual explanation also states that light speed is only marginally less in air compared to vacuum but reduces considerably in glass or water, and defines refractive index in terms of the ratio of speeds in two media, confirming that light slows most in the optically denser medium (glass) among the options given [2]. Therefore, light speed is minimum in glass.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.2 The Refractive Index > p. 149
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.2 The Refractive Index > p. 148