I will show you how to express meanings like "right/wrong", "true/false", "correct/incorrect", "truth/lie", etc. They are all black-and-white opposites.
Somebody is Right
First, how to express that someone is "right" or "wrong", that is, what someone thinks or says is correct or incorrect? Croatian uses two phrases to express this meaning with verb säm:
phrase meaning P je u pravu "P is right" (in his/her opinion) P je u krivu "P is wrong"
Ana je u pravu. "Ana is right."
Ivan i Josip su bili u krivu. "Ivan and Josip were wrong."
Mislim da si u pravu. "I think you're right."
These two phrases (u pravu and u krivu) do not change with number, gender, case etc. Beware, they are used only to express that what a person thinks/says is right or wrong!
Something is Right
However, if you want to express that some thing is "right" or "wrong" (e.g. you took the "right keys", you wrote "wrong answers"), you must use another set or adjectives — Croatian considers this meaning completely unrelated to the previous meaning! They are:
adjective meaning pravi, ispravän "right", "correct" (thing) krivi, pogrešän "wrong", "incorrect" (thing)
Since they are adjectives, they adapt to gender, number and case. For instance:
Uzeo säm krive ključeve. "I took wrong keys."
Našla säm pravi odgovor. "I found the right answer." (female speaking)
Stavila si papire u krivu ladicu. "You have put the papers into a wrong drawer."
Even some person can be "right" or "wrong", it doesn't refer to their opinions, but to qualities, e.g. someone is "right for the job". For instance:
Zaposlili smo pravu osobu. "We have employed the right person."
Adjective ispravän has another meaning: "functional", "working", "not broken"; when used in that meaning, its opposite is neispravän "not functional", "broken"; adjective pokvaren "spoiled, foul" can be used in the meaning "not functional" as well:
Frižider je pokvaren. "The fridge is broken."
Motor je ispravän. "The engine is functional."
Something is Accurate
Next, you might want to express that something is "accurate" or "not accurate": use adjectives točän and netočän. They also mean "exact" and "not exact". Since "accurate" is quite similar to "correct", the adjective točän is used to express "correct" as well:
Prognoza je bila točna. "The forecast was accurate."
Sat je netočän. "The clock is not accurate."
Našla säm točän odgovor. "I found the correct answer." (female speaking)
In Serbian, those adverbs have forms tačän and netačän (e.g. našla säm tačän odgovor)!
Adverbs derived from them — točno and netočno mean "exactly, correctly" and "not exactly, not correctly": they are used very frequently:
Točno je podne. "It's exactly noon."
To je točno. "That's correct." "That's right."
The opposite is often expressed with negation of verb säm:
To nije točno. "That isn't correct."