Which prefix indicates a negative or opposite state, as in 'unable'?

The prefix "un-" is used to indicate a negative or opposite state, as seen in the word "unable," which signifies not being able to do something. When "un-" is attached to a word, it typically negates the meaning of that word. For example, "happy" becomes "unhappy," meaning not happy. This prefix is versatile and commonly used in the English language to create words that express negation.

While the other prefixes listed can imply negativity or opposition as well, they do so in different contexts. For instance, "dis-" often conveys a sense of removal or reversal, but it functions differently depending on the word it attaches to. Similarly, "in-" can also imply negation, but it is used specifically with certain root words, such as "invisible," meaning not visible. The prefix "re-" generally indicates repetition or going back, rather than negation. Thus, "un-" is the clear choice for indicating a negative or opposite state.