Final answer:
The purpose of a story comparing chocolate and vanilla ice cream is to either persuade or inform the reader about each flavor's attributes and possibly lead them to choose a favorite.
Step-by-step explanation:
When reading a story about chocolate ice cream and vanilla ice cream to determine which ice cream is better, the purpose is likely to persuade or inform the reader about the merits or downfalls of each flavor. This type of writing could be seen as a comparative essay or an opinion piece. In such a story, you might find descriptions of the taste, texture, and overall enjoyment factor of both types of ice cream, possibly with the writer taking a side or encouraging the reader to decide which is superior based on the presented arguments.