Final answer:
The concentration of HNO₂ in the buffer solution is 0.115 mM, which directly indicates 0.115 mmol of HNO₂ per liter of solution.
Step-by-step explanation:
The concentration of HNO₂ in the buffer solution is already provided in the question - it is 0.115 mM (millimolar). Since the volume of the buffer solution is 1.0 L, there is no need to perform any additional calculations to determine the concentration of HNO₂.
The concentration represents the amount of HNO₂ in moles per liter (molarity) of solution, and since the provided concentration is in millimolar units, it means 0.115 mmol of HNO₂ is present in every liter of the buffer solution.