The velocity of electromagnetic radiation in a medium of permittivity $\varepsilon $0 and permeability $\mu $0 is given by
${1 \over {\sqrt {{\mu _0}{\varepsilon _0}} }}$
$\sqrt {{{{\mu _0}} \over {{\varepsilon _0}}}} $
$\sqrt {{{{\varepsilon _0}} \over {{\mu _0}}}} $
$\sqrt {{\mu _0}{\varepsilon _0}} $
