The wavelength of light coming from a sodium source is 589 nm. Its wavelength in crown glass having refractive index 1.52 is

387.5 nm

The correct answer is Option (1) → 387.5 nm

Wavelength in a medium: $\lambda_\text{medium} = \frac{\lambda_\text{vacuum}}{\mu}$

Given: $\lambda_\text{vacuum} = 589\ \text{nm}$, $\mu = 1.52$

Wavelength in crown glass:

$\lambda_\text{glass} = \frac{589}{1.52} \approx 387.5\ \text{nm}$

Final Answer: $\lambda_\text{glass} \approx 388\ \text{nm}$