what can enter a room and harm its occupants if the heat exchanger of a furnace is bad?\nhelium\nhydrogen\nca…

Brief Explanations:

Carbon - monoxide is a dangerous gas produced by incomplete combustion. When the heat exchanger of a furnace is bad, carbon - monoxide can leak into the room and harm occupants as it binds to hemoglobin in the blood, preventing normal oxygen transport. Helium is an inert gas and not harmful in normal circumstances. Hydrogen is flammable but not as immediately harmful to health as carbon - monoxide in this context. Magnesium is a solid metal and not a gas that would typically enter a room from a furnace problem.

Answer:

C. carbon monoxide