Words ending in -sion
• If the ending is pronounced as in confusion, then it should be spelled -sion.
Here are some examples : collision ; division ; revision; persuasion ; explosion
• When the ending comes after an -l, it's always spelled -sion :
Example : compulsion ; revulsion ; expulsion ; emulsion ; propulsion.
• When the ending follows an -n or -r, it's often spelled -sion, especially if the word is related to one that ends in -d or -se.
For example: immersion (from immerse) ; comprehension (fromcomprehend)
Nouns based on words that end in -ss or -mit always end in -sion: permission comes (from permitand) discussion comes (from discuss)