Light ray travels from a rarer medium to a denser medium. Which of th…

The correct answer is Option (3) → Frequency of the light increases

The frequency of light is fixed by its source and does not change when light crosses from one medium to another; only the speed and the wavelength change. Going from a rarer to a denser medium the refractive index n increases, so

    \( \displaystyle v = \frac{c}{n} \) decreases, and \( \displaystyle \lambda = \frac{v}{\nu} = \frac{\lambda_0}{n} \) decreases (\( \nu \) constant).

By Snell’s law, with \( n \gt 1 \) for the second medium relative to the first:

    \( \displaystyle \sin i = n\,\sin r \Rightarrow \sin r = \frac{\sin i}{n} \lt \sin i \Rightarrow r \lt i \)

So the speed decreases (1), the wavelength decreases (2) and the angle of incidence is greater than the angle of refraction (4), all correct. The statement that the frequency increases is the incorrect one.

NCERT (2026-27):
Refraction of a Plane Wave – “… The above equation implies that when a wave gets refracted into a denser medium (v₁ > v₂) the wavelength and the speed of propagation decrease but the frequency ν (= v/λ) remains the same.”