You confused us with the word 'mention' - we didn't know what you were asking. You should have said - for example - What is the difference between the pronunciation of 'of' and'off' ? or What is the difference between how we SAY or PRONOUNCE 'of' and 'off'? And - as Jmat has said - 'off' has a /f/ sound, while 'of' has a /v/ sound.

Off is the opposite of 'on' Of you would say when you were talking about a noun that 'belongs' to another thing Eg 4th of July The object of her affection

'Of' ends in a 'v' sound. 'Off' ends in a 'f' sound.

Are you asking; what the difference is between 'of' and 'off'...?