In this scenario, Ethan has been exposed to a chemical substance (oven cleaner) which may have been inhaled or come into contact with his skin and may also cause chemical burns.
Given the symptoms of dizziness, coughing, and headache, the most appropriate treatment by the EMR would be to administer high-flow oxygen while calling a poison control center for advice. This is because inhalation of chemical fumes can affect respiratory function, and providing supplemental oxygen is critical to support his breathing and oxygenation.
Therefore, the correct answer is:
The EMR will likely administer high-flow oxygen while calling a poison control center for advice.