Option 1 -> Malaise refers to a general feeling of discomfort or unease, not an opposite of malignant.
Option 2 -> Toxic means poisonous or harmful, which is similar in meaning to malignant rather than opposite.
Option 3 -> Rare means uncommon or infrequent, which is unrelated to the harmful/dangerous meaning of malignant.
Option 4 -> Benign means harmless or non-threatening, especially in medical contexts where it describes non-cancerous growths.
Hence, Option 4: Benign -> Malignant and benign form a classic antonym pair, particularly in medical terminology where malignant refers to cancerous/dangerous conditions while benign refers to harmless/non-cancerous ones -> correct