The prefix you would add to "inflate" to make an antonym is "de-," resulting in "deflate." This means to decrease in size or volume.
The prefix "ir-" before "regular" would create the antonym "irregular."
You could add the prefix af- to it to make the word affluent.
The prefix you would add to "ordinary" to make it the opposite is "extra-". This would create "extraordinary," which means exceptional or remarkable.
"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."
The prefix is in- The opposite of conspicuous (easily seen) is inconspicuous.
A prefix is an added beginning to a word, which often changes its meaning. If you add the prefix "mis" to spelled, you get the word "misspelled", which means spelled incorrectly. This is, indeed, the antonym, or opposite, of spelled. disable, unable, and enable
"Possibility" doesn't have a prefix. You could add the prefix im- to it to make the word impossibility.
You could add the prefix im- to it to make the word impossible.
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.
A prefix is a group of letters added at the beginning of a word to change its meaning, such as adding "un-" to "happy" to make "unhappy".
You could add the prefix af- to it to make the word affluent.
The prefix for standard is "non-" as in "nonstandard."
"Social" doesn't have a prefix. You could add the prefix un- to it to make the word unsocial.
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.