B

Step 1: Understand the wave properties of light. Light behaves as a wave, and its properties change when it moves between different media.
Step 2: Define the terms denser and rarer medium. A denser medium has a higher refractive index, while a rarer medium has a lower refractive index.
Step 3: Recall the relationship between velocity, frequency, and wavelength of light. The equations governing these properties are:
$$ v = f imes \lambda $$
Where:

• v = velocity of light in the medium
• f = frequency of light
• \lambda = wavelength of light

Step 4: When light travels from a denser medium (higher refractive index) to a rarer medium (lower refractive index), its speed increases since the velocity of light in a medium is given by: $$ v = \frac{c}{n} $$
where $c$ is the speed of light in vacuum and $n$ is the refractive index of the medium. Thus, in a rarer medium, $n$ is less, leading to increased velocity $v$.
Step 5: The frequency (f) of light remains constant when transitioning between media. Therefore, an increase in velocity $v$ will result in an increase in wavelength $\lambda$ because: $$ \lambda = \frac{v}{f} $$
Conclusion: As light passes from a denser medium to a rarer medium, the wavelength of light increases.