Final answer:
The sun appears bigger at sunrise and sunset due to atmospheric refraction and the scattering of light.
Step-by-step explanation:
Assertion: Yes, the sun appears bigger in size at sunrise and sunset compared to during the day.
Reason: This phenomenon is primarily due to atmospheric refraction and the scattering of light.
During sunrise and sunset, the sun is near the horizon, causing its light to pass through a larger portion of Earth's atmosphere. The atmosphere refracts or bends the light, making the sun appear larger. Additionally, the longer path through the atmosphere scatters the shorter blue wavelengths more, leaving the longer red wavelengths to dominate, giving the sun a reddish hue.
Hence, both the Assertion and the Reason are true, and the Reason is a correct explanation of the Assertion. Therefore, the correct answer is option A.