Authority to pass IBS has been issued from station in rear. A. 10 kmph B. 15 kmph C. 25 kmph D. Normal speed

The correct answer is D. Normal speed.

The authority to pass IBS has been issued from station in rear means that the train is now allowed to pass the intermediate block section (IBS). The speed limit for passing an IBS is the normal speed of the train. This is because the IBS is a safe section of track and there is no need to slow down.

Option A, 10 kmph, is incorrect because it is too slow. The normal speed of a train is much higher than 10 kmph.

Option B, 15 kmph, is incorrect because it is still too slow. The normal speed of a train is much higher than 15 kmph.

Option C, 25 kmph, is incorrect because it is too fast. The speed limit for passing an IBS is the normal speed of the train, which is much lower than 25 kmph.