18) In an experiment for determination of refractive index of glass of a prism by i - $\delta$ plot, it was found that a ray incident at angle 35$°$, suffers a deviation of 40$°$ and that it emerges at angle 79$°$. In case that which of the following is closest to the maximum possible value of the refractive index?
(A) 1.5
(B) 1.6
(C) 1.7
(D) 1.8