Final answer:
When a light wave enters a solid, both the wavelength and the speed of the light wave will decrease due to the higher optical density of the solid compared to air or vacuum.
Step-by-step explanation:
If a light wave moves through a solid, its wavelength will decrease and its speed will also decrease. This is because light travels at different speeds through different mediums due to the optical density of the mediums. The speed of light in a vacuum is the fastest, and when it moves into a medium like a solid, which is more optically dense than a vacuum or air, the speed decreases. According to the relationship between speed, wavelength, and frequency given by the equation c = λf (where c is the speed of light, λ is the wavelength, and f is the frequency), if the speed of light decreases, the wavelength also decreases, provided the frequency remains constant. Therefore, the correct answer to what will most likely happen when a light wave moves through a solid is (b) The wavelength will decrease, speed will decrease.