The correct answer is: A. 75 mm
Cant is the difference in elevation between the inner and outer rails of a railway track. It is used to keep trains from derailing on curves. The amount of cant required depends on the radius of the curve and the speed of the train.
In meter gauge railways, the maximum cant permissible is 75 mm. This means that the inner rail can be up to 75 mm higher than the outer rail on a curve. This is to ensure that the train stays on the track and does not derail.
The other options are incorrect because they are not the maximum cant permissible in meter gauge railways. Option B is 90 mm, option C is 140 mm, and option D is 165 mm. These are all higher than the maximum permissible cant of 75 mm.
It is important to note that the maximum cant permissible may vary depending on the country or railway company. It is always best to check the local regulations before operating a train on a meter gauge railway.