The correct answer is A. 1 in 250.
The ruling gradient is the maximum permissible gradient on a railway line. It is the steepest gradient that can be safely negotiated by trains. The steepest gradient permissible on a 2.5° curve for Broad Gauge line having ruling gradient of 1 in 200 is 1 in 250. This is because the centrifugal force acting on a train on a curve is proportional to the square of the speed of the train and the radius of the curve. The steeper the curve, the greater the centrifugal force. If the gradient is too steep, the centrifugal force will be greater than the force of gravity, and the train will derail.
Option B is incorrect because it is not a safe gradient for a 2.5° curve. Option C is incorrect because it is not a safe gradient for a Broad Gauge line. Option D is incorrect because it is not a safe gradient for a line with a ruling gradient of 1 in 200.