- A) A very small opaque object does change the straight path of light due to diffraction. Light bends around the edges of small objects or passes through small apertures, a phenomenon explained by the wave nature of light. The statement "does not change" is incorrect in the context of diffraction. - C) The mass density of kerosene is indeed less than that of water, which is why kerosene floats on water. This statement is correct. - D) Optical density is a measure of how much a medium slows down light and hence how much it can bend light (refraction). A higher optical density generally implies a higher refractive index. While reflection is also related to the refractive index difference at the boundary between two media, the ability to reflect light is related to the difference in optical densities of the media. This statement is generally accepted in the context of optics discussions comparing different media. This statement is correct.