Refraction: Light slows in denser media

Steps:

• Light travels from air (rarer medium, n≈1) to glass (denser medium, n>1).
• Refractive index n = c/v, where c is speed in vacuum and v is speed in medium.
• In glass, n increases, so v decreases compared to air.
• Frequency f remains constant; wavelength λ = v/f thus decreases.

Why B is correct:

• The speed decreases because the refractive index of glass (n≈1.5) is greater than air's (n≈1), per n = c/v.

Why the others are wrong:

• A: Frequency remains unchanged as it's determined by the source and invariant across media boundaries.
• C: Wavelength decreases since v drops while f stays constant (λ = v/f).
• D: Wavelength changes due to the speed reduction in glass.

Final answer: B