Option 1 -> Harmless means not causing harm or damage, which directly matches the meaning of innocuous.
Option 2 -> Dangerous is the opposite of innocuous, as it means likely to cause harm.
Option 3 -> Poisonous means toxic or harmful, making it an antonym rather than a synonym.
Option 4 -> Soft refers to texture or gentleness, not the absence of harm.
Hence, Option 1: Harmless -> INNOCUOUS means "not harmful or offensive," making harmless the perfect synonym as both words convey the idea of being safe and causing no damage -> correct