Which term refers to something that is unharmful or mild?

The term "innocuous" refers to something that is harmless or mild, making it the most appropriate choice in this context. It conveys a sense of safety and a lack of potential negative effects. For example, an innocuous remark is one that is not intended to offend or cause any harm. This word is often used to describe substances, behaviors, or actions that are not dangerous or threatening.

In contrast, the other terms carry negative connotations. "Noxious" typically refers to harmful or toxic substances that can cause injury or harm, while "pernicious" describes something that is subtly harmful or destructive. "Malignant" is often used in medical contexts to describe tumors that are cancerous and potentially threatening to health. Therefore, "innocuous" stands out as the correct term associated with being unharmful or mild.