**Core Concept**
Diabetic ketoacidosis (DKA) is a life-threatening complication of diabetes characterized by hyperglycemia, metabolic acidosis, and ketosis. Insulin therapy is essential to correct hyperglycemia and ketosis, but other interventions are also crucial to manage the condition effectively.

**Why the Correct Answer is Right**
In DKA, the body produces ketones as an alternative source of energy due to insulin deficiency. However, ketone production leads to metabolic acidosis, which can be life-threatening if not managed promptly. Administering sodium bicarbonate (NaHCO3) helps to correct acidosis by increasing the bicarbonate levels in the blood, thereby reducing the acidity. This is crucial in the initial management of DKA, especially in patients with severe acidosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Potassium supplementation is not typically begun immediately in DKA. While potassium levels may be low due to insulin deficiency, administering potassium can lead to cardiac arrhythmias and is best started after glucose levels have normalized and insulin therapy has been established.
**Option B:** Glucagon is not indicated in DKA. In fact, glucagon can worsen the condition by promoting glycogenolysis and gluconeogenesis, leading to further hyperglycemia.
**Option C:** Metformin is not indicated in DKA. Metformin can worsen lactic acidosis, which can occur in the setting of DKA.

**Clinical Pearl / High-Yield Fact**
In the initial management of DKA, it's essential to remember that insulin therapy should be started with a bolus dose of 0.1 units/kg to rapidly lower glucose levels, followed by a continuous infusion of 0.05-0.1 units/kg/hour to maintain euglycemia.

**Correct Answer:** C.