Asource emits monochromatic light of wavelength 495 nm in air. when the light passes through a liquid, its wavelength reduces to 434 nm what is the liquid's index of refraction? a. 1.14 b. 1.49 c. 2.03 d. 1.26 e. 1.33

By definition, the refractive index is
n = c/v
where c =  3 x 10⁸ m/s,  the speed of light in vacuum
v = the speed of light in the medium (the liquid).

The frequency of the light source is
f = (3 x 10⁸ m/s)/(495 x 10⁻⁹ m) = 6.0606 x 10¹⁴ Hz

Because the wavelength in the liquid is 434 nm = 434 x 10⁻⁹ m, 
v = (6.0606 x 10¹⁴ 1/s)*(434 x 10⁻⁹ m) = 2.6303 x 10⁸ m/s

The refractive index is (3 x 10⁸)/(2.6303 x 10⁸) = 1.1406

  a.  1.14

The answers would be: 1: the liquid only contains one compound4: the liquid is a pure substance