**Core Concept**
The normal acid level in the stomach is maintained by a delicate balance between acid production and neutralization. This balance is crucial for digestion and preventing gastric mucosal damage. The stomach lining secretes mucus and bicarbonate to neutralize the acidic environment.

**Why the Correct Answer is Right**
The correct answer is pH 1.5-3.5. This acidic environment is necessary for the activation of pepsin, a digestive enzyme that breaks down proteins into smaller peptides. The parietal cells in the stomach lining secrete hydrochloric acid (HCl) in exchange for chloride ions, which helps to maintain the acidic pH. The acidic environment also denatures proteins, making them more susceptible to enzymatic digestion.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the normal pH range of the stomach is more acidic than neutral.
**Option B:** This option is incorrect because the pH range of the stomach is not close to the slightly alkaline pH of the small intestine.
**Option C:** This option is incorrect because the pH range of the stomach is not significantly different from the acidic pH of the duodenum.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the stomach lining secretes mucus and bicarbonate to protect itself from the acidic environment, which can cause ulcers and other damage if not properly regulated.

**Correct Answer:** C.