Choose the misspelt word from the given options.

The correct option is Supercideous.

Let us analyze the spelling and meaning of each word given in the options:
1. Conscientious: Spelled correctly. It means wishing to do one's work or duty well and thoroughly.
2. Mischievous: Spelled correctly. It refers to someone causing or showing a fondness for causing trouble in a playful way.
3. Bureaucracy: Spelled correctly. It refers to a system of administration where decisions are made by state officials.
4. Supercideous: Spelled incorrectly.

The correct spelling of this word is Supercilious. It is an adjective that means behaving or looking as though one thinks one is superior to others.