Final answer:
The correct synonym for "benign" is "innocuous," which also denotes something harmless and not likely to cause injury.
Step-by-step explanation:
The synonym for "benign" when used as an adjective is c) Innocuous. "Benign" implies that something is gentle, harmless, or not causing damage or harm.
The antonyms of "benign," such as "harmful," "malignant," and "malevolent," suggest the opposite meaning, indicating something that causes harm or is intended to be hostile.
Therefore, "innocuous" is the correct synonym as it also means something that is not likely to offend or cause harm.