When light passes from one medium to another, such as from air to glass, it can undergo refraction. Refraction occurs because light travels at different speeds in different mediums.

Option 1 suggests that the density of glass is higher than that of air, which is not entirely accurate. Density refers to the mass of a substance per unit volume, and while the density of glass is generally higher than air, it does not directly explain why light gets refracted.

Option 2 states that light cannot be reflected from a glass surface, which is not true. Reflection and refraction are separate phenomena. Refraction refers to the bending of light as it passes from one medium to another, while reflection refers to the bouncing back of light from a surface.

Option 3 proposes that glass absorbs energy from light rays, which is not the main reason for refraction. While some energy may be absorbed by the glass, it does not primarily cause refraction.

Option 4 correctly states that the speed of light in glass is less than the speed of light in air. The change in speed is what causes the bending of light rays as they enter the glass, leading to refraction. This change in speed occurs due to the difference in optical density between air and glass.