Which of the following instruments would typically measure the combustion quality in a boiler?

The correct answer is a gas analyzer because it is specifically designed to measure the concentration of various gases produced during combustion, such as carbon monoxide, carbon dioxide, nitrogen oxides, and oxygen. This data is essential for evaluating combustion efficiency and ensuring that the boiler operates within safe and environmentally compliant parameters. Monitoring these gases helps in assessing the combustion quality, identifying any adjustments needed for optimizing performance, and detecting any hazardous emissions that could pose a danger to both equipment and personnel.

In contrast, a thermometer measures temperature, providing information pertinent to the thermal performance of the boiler but not directly assessing combustion quality. A pressure gauge measures the pressure within the system, which is important for safety and operational purposes but does not give insight into the combustion process itself. A megohmmeter is used for insulation resistance testing in electrical systems and does not relate to combustion measurement at all. Thus, the specificity and functionality of a gas analyzer make it the appropriate choice for assessing combustion quality in a boiler system.