Final answer:
The risk of adverse reactions to penicillin G potassium in a client with pneumonia is increased by a known allergy to penicillin or beta-lactam antibiotics and renal impairment.
Step-by-step explanation:
An assessment finding that increases the risk of adverse reactions in a client being treated with penicillin G potassium intravenously for pneumonia is a known allergy to penicillin or other beta-lactam antibiotics. Allergies can lead to serious or even life-threatening reactions. These reactions may present as rash, hives, itching, difficulty breathing, or anaphylaxis. Additionally, clients with renal impairment may have increased risk due to the potential for drug accumulation and toxicity. Hence, it's vital for healthcare providers to review the patient's history for allergies and assess kidney function before administering penicillin.