In the following sentence, four words have been marked in bold. One of these words may either be spelled incorrectly or used in an inappropriate context. Identify the incorrect word.

It is reasonable to expect that the frequent occurrance of hurricanes in the region would cause a mass departure of inhabitants to a place with a gentler environment.

The correct option is occurrance.

Let us analyze the words highlighted in bold within the sentence to identify the error:
1. hurricanes - Spelled correctly. It refers to severe tropical storms.
2. departure - Spelled correctly. It refers to the act of leaving a place.
3. environment - Spelled correctly. It refers to the surroundings or conditions in which a person, animal, or plant lives.
4. occurrance - Spelled incorrectly.

The correct spelling of the word is occurrence (ending with "-ence" instead of "-ance").

Therefore, the word occurrance is the incorrectly spelled word in the sentence.