**Core Concept**
Sodium nitrate poisoning occurs when excessive amounts of sodium nitrate are ingested, leading to methemoglobinemia, a condition characterized by the formation of methemoglobin, a form of hemoglobin that cannot bind oxygen. The antidote for sodium nitrate poisoning is a medication that can reverse this process by reducing methemoglobin levels.

**Why the Correct Answer is Right**
The correct antidote for sodium nitrate poisoning is methylene blue. Methylene blue works by donating electrons to methemoglobin, thereby converting it back to normal hemoglobin. This process is facilitated by the enzyme NADH methemoglobin reductase, which is present in red blood cells. Methylene blue is a potent reducing agent that can rapidly decrease methemoglobin levels, thereby alleviating the symptoms of sodium nitrate poisoning.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a known antidote for sodium nitrate poisoning.
**Option B:** This option is incorrect as it is not a medication that is used to treat methemoglobinemia.

**Clinical Pearl / High-Yield Fact**
Methylene blue is a versatile medication that can be used to treat a variety of conditions, including methemoglobinemia, septic shock, and certain types of anaphylaxis. It is essential for postgraduate medical students to be familiar with the indications and contraindications of methylene blue.

**Correct Answer:** C. Methylene blue