Which of the following is a limitation for keys in a dictionary?

In a dictionary, keys must be unique, meaning that no two entries can have the same key. If you attempt to add a key that already exists in the dictionary, the new value associated with that key will replace the existing value. This uniqueness requirement is fundamental to how dictionaries operate, as they rely on a key-value pairing system that allows for fast lookups, updates, and deletions.

This distinctive feature ensures that each key points to exactly one value, preventing any ambiguity regarding the association between keys and values. Understanding the uniqueness requirement of dictionary keys is crucial for effective data management and retrieval in Python programming.