Final answer:
An observer on Mercury would see the Sun rise in the east. Unique orbital characteristics of Mercury, such as its eccentric orbit and lack of atmosphere, make its sunrises and sunsets appear rapidly with noticeable changes in the Sun's size and speed throughout the day.
Step-by-step explanation:
Just like on Earth, on Mercury an observer would see the Sun rise in the east. However, Mercury has some unique astronomical phenomena due to its eccentric orbit. For example, at the location of Caloris, which is a large crater on Mercury, the Sun appears much smaller at sunrise and gets larger as it rises higher in the sky. The apparent motion of the Sun also changes throughout the day as Mercury's orbital speed varies due to its eccentric orbit in accordance with Kepler's laws.
Mercury's orbit around the Sun is indeed very eccentric, and therefore the distance between Mercury and the Sun changes significantly, affecting the apparent size and motion of the Sun in the sky. When closest to the Sun, Mercury moves faster in its orbit. Consequently, over one Mercurian day (which is equivalent to 176 Earth days), the Sun looks largest at noon and nearly motionless but becomes smaller and moves more rapidly as it sets towards evening.
Since Mercury has no atmosphere to scatter light, sunrises and sunsets happen very rapidly compared to Earth. The phenomenon of the Sun rising in the east and setting in the west is common to most planets in our solar system, including Mercury, due to their rotation around their axes.