Which keyword is used to check if a specific key exists in a dictionary?

The correct choice is "in," which is the keyword used in Python to check for the existence of a specific key in a dictionary. When you use "in," you can directly evaluate whether a key is present in the dictionary's keys. For example, if you have a dictionary named my_dict, you can check if a key called key_name exists by using the expression key_name in my_dict. This will return True if the key is found and False otherwise.

The other options don't serve this purpose in Python. "exists" and "contains" are not keywords in Python that can be used to check for the presence of keys in dictionaries. "is" is a keyword used for identity comparisons, checking if two references point to the same object in memory, and does not relate to key existence in dictionaries. Thus, "in" is the appropriate keyword for this operation.