Final answer:
The Andromeda Galaxy was originally classified as a nebula due to its faint appearance in early telescopes, but it is actually an entire galaxy separate from the Milky Way. Hence the correct answer is option C
Step-by-step explanation:
The question asks which of the following objects was originally classified as a nebula. Among the given choices, the Andromeda Galaxy was initially classified as a nebula. In early astronomical observations, the Andromeda Galaxy appeared as a faint and indistinct object, leading to its classification as a nebula. It was thought that if these nebula-like objects were nearby, they could be gas clouds or star clusters within our Galaxy. However, as telescopic technology advanced, it became clear that the Andromeda Galaxy is actually a separate galaxy far beyond the edge of the Milky Way, containing billions of stars.
The other objects listed, such as the Orion Nebula and the Ring Nebula, were correctly identified as gaseous nebulae, which are clouds of gas and dust within our Galaxy. The Hercules Globular Star Cluster is a collection of tightly packed stars, and Pluto is a dwarf planet in our solar system.
Hence the correct answer is option C