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Coronal holes (CHs) regions are dark in comparison to the quiet-Sun (QS) atthe coronal temperatures. However, at chromospheric and transition region (TR)temperatures, QS and CHs are hardly distinguishable. In this study we have usedthe \ion{Mg}{2}~2796.35~{\AA} spectral line recorded by the Interface RegionImaging Spectrometer (IRIS) to understand the similarities and differences inthe QS and CH at chromospheric levels. Our analysis reveals that the emissionfrom \ion{Mg}{2}~k3 \& k2v that originates in the chromosphere is significantlylower in CH than in QS for the regions with similar magnetic field strength.The wing emissions of \ion{Mg}{2}~k that originates from the photosphericlayer, however, do not show any difference between QS and CH. The difference in\ion{Mg}{2}~k3 intensities between QS and CH increases with increasing magneticfield strength. We further studied the effects of spectral resolution on thesedifferences and found that the difference in the intensities decreases withdecreasing spectral resolution. For a resolution of 11~{\AA}, the differencecompletely disappears. These findings are not only important for mass andenergy supply from the chromosphere to the corona but also provides essentialingredients for the modelling of the solar spectral irradiance for theunderstanding of the Sun-climate relationships.

Quiet-Sun and Coronal Hole in \ion{Mg}{2}~k line as observed by IRIS