Which of these is not a symptom of hydrogen chloride exposure?

A skin rash is not commonly associated with hydrogen chloride exposure. Hydrogen chloride is a corrosive gas that, when dissolved in water, forms hydrochloric acid. The primary symptoms of exposure to hydrogen chloride include respiratory issues such as coughing and throat irritation due to its irritating properties. The acid burn occurs when it comes into contact with skin or mucous membranes, leading to chemical burns rather than a general skin rash. Therefore, the other symptoms listed—acid burn, cough, and throat irritation—are directly related to exposure to hydrogen chloride and indicate its harsh effects on the respiratory system and tissue. In contrast, a skin rash typically suggests an allergic reaction or irritation from a different source rather than direct exposure to this particular chemical.