Final answer:
An unpolarized beam of light can be split into two polarized beams by using a birefringent material like calcite, as it has different refraction indices for different light polarizations. Therefore, the correct option is 1) a birefringent material like calcite.
Step-by-step explanation:
An unpolarized beam of light of a single pure color can be split into two separate beams by using a birefringent material like calcite. Birefringent materials possess the unique characteristic of having different indices of refraction for different polarizations of light.
When unpolarized light enters a birefringent crystal such as calcite, it is split into two rays: the ordinary ray, which behaves as expected, and the extraordinary ray, which does not follow Snell's law. This results in two beams that are polarized at perpendicular angles to each other.
Some birefringent materials may also exhibit dichroic properties, which means they can preferentially absorb one of the polarizations, leading to the production of polarized light.
Therefore, the correct answer to the student's question is option 1) a birefringent material like calcite. Neither the human retina, metal-ceramic inversion, nor a thin layer of oil can split an unpolarized beam of light into two separate polarized beams.