Question

a smoke test is used to determine the amount of soot in flue gases. soot in a heat exchanger. carbon dioxide in flue gases. carbon monoxide in flue gases.

Explanation:

A smoke test is specifically designed to measure the quantity of soot (fine black particles of carbon) present in flue gases. Flue gases are the gases that exit from a combustion process (like in a furnace or boiler) through a flue. Soot in flue gases is what the smoke test detects. The other options are incorrect: a smoke test is not for soot in a heat exchanger (it's about flue gases), and it doesn't measure carbon dioxide or carbon monoxide (those have other testing methods).

Answer:

A. soot in flue gases.