A uniform disck rolls from rest from height `y_(1)` down the side of a fixed trough whose vertical dimension `y` is given by the equation `y=kx^(2)`. The disc does not slip from A to B, but the surface of the trough is frictionless from B C (see figure). The disc reaches height `y_(2)`. `(3y_(2))/(y_(1))` is (Assume radius of disc to be very small compared to `y_(1)` & `y_(2)`)

Options

A. In rock salt structure `a=2(r_("cation")+r_("anion"))`. Where `a=` edge length of cube
B. In `CsCl` structure `a=2/(sqrt(3))(r_("cation")+r_("anion"))`. Where `a=` edge length of cube
C. In antifluorite structure `a=4/(sqrt(3))(r_("cation")+r_("anion"))`. Where `a=` edge length of cube
D. In ` NaCl` structure `a=2/(sqrt(3))(r_("cation")+r_("anion"))`. When `a=` edge length of cube