Which of the following is a severe symptom of lead poisoning?

Respiratory arrest is a severe symptom of lead poisoning because lead affects multiple systems in the body, including the nervous system, which can lead to significant complications such as seizures, altered mental status, and even respiratory failure. Lead poisoning primarily affects children, but adults can also suffer serious effects. High levels of lead in the bloodstream can cause profound symptoms due to toxicity in the spinal cord and brain, resulting in respiratory muscle paralysis and compromised airway control, leading to respiratory arrest.

The other choices, such as dry cough and nausea, are more mild and nonspecific symptoms that can be associated with a variety of conditions. Increased appetite is not typically related to lead poisoning; in fact, one might see reduced appetite as the body reacts to the systemic effects of the poisoning. Such symptoms would not indicate the severity typically associated with lead toxicity, which can lead to life-threatening situations if not addressed promptly.