The Speed of Light Generally Decreases When It Passes Through $\eta$

The speed of light generally decreases when it passes through media other than a vacuum.The speed, v, is approximately c (2.998 *10⁸ m/s) divided by a quantity called the medium's refractive index, $\eta$ .In which of the following would the frequency of 193 nm light be the lowest? ( $\nu$ = c/ $\eta$ ; c = $\lambda$$\nu$ )

A) hydrogen, $\eta$ = 1.0001
B) carbon tetrachloride, $\eta$ = 1.461
C) silicone oil, $\eta$ = 1.520
D) water, $\eta$ = 1.3330
E) diamond, $\eta$ = 2.419