The correct answer is: B. 1.5:1
The side slope of embankments for a railway track is generally taken as 1.5:1. This means that for every 1 foot of vertical rise, there should be 1.5 feet of horizontal run. This slope is designed to provide stability for the embankment and to prevent it from sliding.
The other options are incorrect because they are not steep enough to provide adequate stability for the embankment. A slope of 1:1 would be too flat and would not be able to withstand the weight of the railway track and the trains that travel on it. A slope of 2:1 would be too steep and would be difficult to construct and maintain.
The side slope of an embankment is an important factor in its design and construction. The slope must be steep enough to provide stability, but not so steep that it is difficult to construct or maintain. The slope must also be compatible with the surrounding terrain.