Correct Answer  Option 4 : 10.0 cm
Explanation:
The cant at which loads on two rails are equal is called equilibrium cant.
Cant deficiency is the difference between equilibrium cant necessary for maximum permissible speed on a curve and the actual cant provided.
Given,
Speed = 120 kmph > 100 kmph
∴ Cant Deficiency for BG Track for V > 100 kmph is 100 mm = 10 cm
Maximum cant deficiency:
Gauge

For speed
up to 100
kmph

For speed
> 100
kmph

B. G

75 mm

100 mm

M. G

50 mm

–

N. G

40 mm

–

Equilibrium cant \(= \frac{{{\rm{G}}{{\rm{V}}^2}}}{{127{\rm{R}}}}\)
V  Design speed (kmph)
R  Radius of curvature (m)
For B.G track G = 1.676
\(\begin{array}{l} {\rm{Cant}} = \frac{{1.676{\rm{\;}}{{\rm{V}}^2}}}{{127{\rm{\;R}}}}{\rm{m}}\\ {\rm{e}} = \frac{{1.315{\rm{\;}}{{\rm{V}}^2}}}{{\rm{R}}}{\rm{cm}} \end{array}\)