The dielectric constant of air is 1.006. The speed of electromagnetic wave travelling in air is $a \times 10^8 ms^{-1}$, where a is about:

3 3.88 2.5 3.2

3

The speed of the electromagnetic wave in vacuum is $\mathrm{c}=\frac{1}{\sqrt{\mu_0 \varepsilon_0}}=3 \times 10^8 \mathrm{~ms}^{-1}$ Air acts almost as vacuum, therefore  $3 × 10^8=a × 10^8$ or a = 3 (approximately)