**Core Concept**
The patient has experienced severe H2SO4 (sulfuric acid) poisoning, leading to hypotension and restlessness. Sulfuric acid is a strong acid that can cause severe burns, systemic toxicity, and metabolic disturbances.

**Why the Correct Answer is Right**
The next step in managing acid poisoning is to administer sodium bicarbonate (NaHCO3) to help neutralize the acid and stabilize the patient's pH levels. Sodium bicarbonate works by increasing the bicarbonate levels in the blood, which helps to buffer the acid and prevent further acidosis. This is particularly important in cases of severe acid poisoning, where the patient's acid-base balance is severely disrupted.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering activated charcoal is not effective in acid poisoning as the acid has already been absorbed into the bloodstream. Moreover, activated charcoal is more effective in cases of poisoning with substances that have a high volume of distribution.

**Option B:** Administering N-acetylcysteine is effective in acetaminophen (paracetamol) poisoning, not acid poisoning. N-acetylcysteine works by replenishing glutathione levels and protecting the liver from damage.

**Option C:** Administering atropine is not indicated in acid poisoning as the primary concern is acid-base imbalance and hypotension, not bradycardia or excessive salivation.

**Option D:** Administering calcium gluconate is not effective in acid poisoning as the primary concern is acid-base imbalance, not hypocalcemia.

**Clinical Pearl / High-Yield Fact**
In cases of acid poisoning, it is essential to remember that the patient's acid-base status can deteriorate rapidly, and prompt treatment with sodium bicarbonate is crucial to prevent further complications.

**Correct Answer: C. Administer sodium bicarbonate.**