Final answer:
In a boiler plant with two 250 horsepower boilers connected to the same common header, a chief engineer license would be required to be in charge of the plant.
Step-by-step explanation:
In a boiler plant with two 250 horsepower boilers connected to the same common header, the engineer required to be in charge of the plant would most likely need a a) chief engineer license. A chief engineer license is typically the highest level of licensure in the field of engineering and is required for overseeing large-scale facilities like boiler plants. This license ensures that the engineer has the necessary knowledge and skills to manage and maintain the boilers and associated systems.