What part of speech is expulsion?
http://www.google.com/search?q=logarithms&rlz=1C1AVSX_enUS414US423&oq=logarithms&aqs=chrome..69i57j0l5.3977j0j8&sourceid=chrome&espv=210&es_sm=122&ie=UTF-8#es_sm=122&espv=210&q=expulsion+definition
A big clue is that ends in -ion. Only one part of speech uses this suffix.