The ratio of the refractive index of red light to blue light in air is

The correct option is C

Less than unity

Refractive Index:

1. The refractive index is a measurement of how much a light ray bends as it passes through different mediums.

Step 1: Formula Used:

$\mu =\frac{c}{n\lambda }$

Here $\mu$is the Refractive index,

$c$ is the speed of light in vacuum,

$\lambda$ is Wavelength of light,

$n$ is the frequency of light

Step 2: Calculations:

Let ${\lambda }_r$ be the wavelength of red light,

and ${\lambda }_b$ be the wavelength of blue light.

In the visible light spectrum wavelength of the red light is larger than the wavelength of blue light

${\lambda }_r>{\lambda }_b$

From the relation between wavelength and refractive index

$\mu =\frac{c}{n\lambda }$

We can observe that Wavelength is inversely proportional to refractive index.

${\mu }_b>{\mu }_r$

$\frac{{\mu }_r}{{\mu }_b}<1$

So we obtained that the ratio of the refractive index of the red light to the refractive index of the blue light is smaller than 1.

Final Answer: Hence option (c)less than unity is correct.