Multiple choice

The most poisonous gas in absence of oxygen is ____________.

  1. CO2 + H2O

  2. CO

  3. N2

  4. CO2

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Carbon monoxide (CO) is highly poisonous because it binds to hemoglobin in red blood cells 200+ times more strongly than oxygen, preventing oxygen transport and causing asphyxiation. CO2 is not poisonous in normal concentrations but causes suffocation by displacing oxygen. Nitrogen is inert.