In an experiment for determination of refractive index of glass of a prism by $i -\sigma$ , plot, it was found that a ray incident at angle $35 ^{\circ}$, suffers a deviation of $40^{\circ}$ and that it emerges at angle $79^{\circ}$.In that case which of the following is closest to the maximum possible value of the refractive index?

Question

$\begin{array}{1 1} (1) 1.5 \\ (2) 1.6 \\ (3) 1.7 \\(4) 1.8 \end{array}$