**Core Concept**
Potassium levels in the body are regulated by various mechanisms, including hormonal influences and renal function. The kidneys play a crucial role in maintaining potassium balance by adjusting the amount of potassium excreted in the urine. Certain medications and conditions can affect potassium levels by altering renal function or influencing potassium flux across cell membranes.

**Why the Correct Answer is Right**
The correct answer, **β2 agonists**, increase potassium levels in the body by stimulating the renal potassium secretory pathways. **β2 agonists** activate the **adenylyl cyclase** enzyme in the renal collecting ducts, leading to an increase in cyclic AMP (cAMP) levels. This increase in cAMP activates the **Na+K+2Cl- cotransporter**, which in turn increases potassium secretion into the urine. This results in a decrease in potassium reabsorption and an increase in potassium excretion, ultimately leading to an increase in serum potassium levels.

**Why Each Wrong Option is Incorrect**
**Option A:** **β blockers** actually decrease potassium levels by inhibiting the **adenylyl cyclase** enzyme and reducing cAMP levels, which decreases potassium secretion into the urine.

**Option B:** **Thiazide diuretics** decrease potassium levels by increasing sodium delivery to the distal tubules, which increases potassium secretion into the urine.

**Option C:** **Loop diuretics** decrease potassium levels by increasing sodium and chloride delivery to the distal tubules, which increases potassium secretion into the urine.

**Clinical Pearl / High-Yield Fact**
The **β2 agonists** can cause hyperkalemia, especially in patients with renal impairment. This is an important consideration when prescribing these medications to patients with underlying kidney disease.

**Correct Answer:** C. **β2 agonists** increase the potassium level in the body by stimulating the renal potassium secretory pathways.