The total gap on both sides between the inside edges of wheel flanges and gauge faces of the rail is kept as A. 10 mm B. 13 mm C. 16 mm D. 19 mm

Option A is incorrect because it is too small. If the gap is too small, the wheels may rub against the rails and cause derailment.

Option B is incorrect because it is too large. If the gap is too large, the wheels may not have enough traction and the train may derail.

Option D is incorrect because it is not a valid option.