Final answer:
The oxygen concentration delivered by a NRB with a flow rate of 12-15 L/min is approximately 100%.
Step-by-step explanation:
The oxygen concentration delivered by a Non-Rebreather Mask (NRB) with a flow rate of 12-15 L/min is approximately 100%.
A NRB mask is designed to deliver a high concentration of oxygen to the patient by preventing the rebreathing of exhaled air. The mask is connected to an oxygen source with a flow rate of 12-15 L/min, which ensures that the mask is always filled with fresh oxygen.
Therefore, the option d. 100% is the correct answer.