The prefix you would add to "ordinary" to make it the opposite is "extra-". This would create "extraordinary," which means exceptional or remarkable.
You could add the prefix af- to it to make the word affluent.
The prefix you would add to "inflate" to make an antonym is "de-," resulting in "deflate." This means to decrease in size or volume.
You could add the prefix un- to it to make the word unreliable.
"Cost" doesn't have a prefix. You could add the prefix ac- to it to make the word "accost."
The prefix for standard is "non-" as in "nonstandard."
"Possibility" doesn't have a prefix. You could add the prefix im- to it to make the word impossibility.
You could add the prefix af- to it to make the word affluent.
You could add the prefix ad- to it to make the word advantage.
You could add the prefix sur- to it to make the word surround.
You could add the prefix im- to it to make the word impossible.
The current prefix is ex-. You could add the prefix in- to it to make the word inexcusable.
The current prefix is im-. You could add the prefix un- to it to make the word unimportant.
"Social" doesn't have a prefix. You could add the prefix un- to it to make the word unsocial.
The prefix you would add to "inflate" to make an antonym is "de-," resulting in "deflate." This means to decrease in size or volume.
You could add the prefix mis- to it to make the word misfits.
The prefix 'im' can added to make the word impolite.
You could add the prefix un- to it to make the word unreliable.