The speed of light in air, if an electromagnetic wave is travelling in air whose dielectric constant is $k = 1.006$, will be :

$\begin {array} {1 1} (a)\;3 \times 10^8 m/s & \quad (b)\;3.88 \times 10^8 m/s \\ (c)\;2.5 \times 10^8 m/s & \quad (d)\;4.6 \times 10^8 m/s \end {array}$

Note that the question asks the speed of light in air, but data about an EM wave is given,
which does not, by any way affect the speed of light in air.
Ans : (a)