**Core Concept**
Methemoglobinemia is a condition characterized by an abnormal amount of methemoglobin in the blood, a form of hemoglobin that cannot bind oxygen. It can be caused by various factors, including certain medications, toxins, and genetic disorders. Methemoglobinemia can lead to tissue hypoxia and requires prompt treatment.

**Why the Correct Answer is Right**
The correct treatment for methemoglobinemia involves administering methylene blue, a drug that acts as a reducing agent and converts methemoglobin back to normal hemoglobin. Methylene blue works by donating electrons to the oxidized iron in methemoglobin, thereby reducing it to its normal ferrous state. This process is facilitated by the enzyme NADPH-dependent methemoglobin reductase.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because vitamin E has antioxidant properties and does not have a direct role in reducing methemoglobin. It may even exacerbate the condition in some cases.
**Option B:** This option is incorrect because folic acid is essential for DNA synthesis and repair but does not have a direct effect on methemoglobin levels.
**Option C:** This option is incorrect because prilocaine, a local anesthetic, can actually cause methemoglobinemia as a side effect, rather than treating it.

**Clinical Pearl / High-Yield Fact**
It's essential to note that methylene blue should be used with caution in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, as it can exacerbate hemolysis in these individuals.

**Correct Answer: C. Methylene blue**