Final answer:
The 'Update' option is not available in the Union tool, while 'Append', 'Combine', and 'Intersect' are commonly associated with data combination methods.
Step-by-step explanation:
The option that is not available for combining data in the Union tool is Update. The Union tool typically has options such as Append, which adds rows of data from one dataset to another, and Combine, which can add new columns from one dataset to another if they share at least one field in common. Intersect is another method used in set operations, but it's not typically a function of the Union tool; rather, it's used in scenarios where the common elements of sets are identified. The Update function is more associated with database operations that modify existing records rather than combining datasets.