The correct answer is A) comparator type mist detector. A comparator type mist detector is a device used to detect the presence and concentration of mist or fog in the atmosphere. This type of device is often used in marine applications, such as on ships and boats, to monitor environmental conditions and ensure safe navigation. The other answer choices are incorrect because: B) Ringelmann exhaust gas analyzer is used to measure the opacity of exhaust emissions, not mist or fog. C) reflective type explosion meter is used to detect the presence of explosive gases, not mist or fog. D) exhaust gas vapor condenser is used to remove water vapor from exhaust gases, not to detect mist or fog.