Incorrect spelling


Incorrect spelling, explanation: convertion is incorrect. The base word of conversion is convert, so it may seem counterintuitive to change the t into s, but this is the case for many words built in a similar way, as the spelling with t would lead speakers to believe that pronunciation also contains t, while the pronunciation is definitely with s.

Correct spelling


Correct spelling, explanation: conversion is created by adding the noun-creating suffix -ion to the verb convert. In this case, the process requires the word to change slightly and to change the t into s, as it’s more fitting to the pronunciation.

Definition of conversion:
1. Turning one thing into another
The conversion of a DOC file into a PDF file is really simple.
2. The change in one’s religious beliefs
His sudden conversion to Christianity surprised his whole family.