If \[{{\mu }_{_{0}}}\] be the relative permeability and \[{{K}_{0}}\] the dielectric constant of a medium, its refractive index is given by [MNR 1995]

• A.            \[\frac{1}{\sqrt{{{\mu }_{0}}{{K}_{0}}}}\]                    
• B.  \[\frac{1}{{{\mu }_{0}}{{K}_{0}}}\]
• C.            \[\sqrt{{{\mu }_{0}}{{K}_{0}}}\]                                       
• D.            \[{{\mu }_{0}}{{K}_{0}}\]