Final answer:
The doorbell circuit installed in a dwelling unit is considered to be a Class 2 circuit when supplied by a 120/24 V, 40 VA Class 2 transformer. This statement is true.
Step-by-step explanation:
The statement is true.
A class 2 circuit is a low-voltage circuit that is supplied by a class 2 transformer. In this case, the doorbell circuit is supplied by a 120/24 V, 40 VA class 2 transformer. The 120/24 V voltage rating indicates that the primary side of the transformer receives 120 V and steps it down to 24 V on the secondary side. The 40 VA power rating indicates the maximum power the transformer can deliver to the circuit.