The total length of a runway is 1000 m. The elevation at distance 0,200 m, 400 m, 600 m, 800 m and 1000 m are 100.0 m, 99.2 m, 101.0 m, 101.8 m, 101.4 m and 101.0 m respectively. The effective gradient of runway will be. A. 0.10 % B. 0.26 % C. 0.43 % D. 0.65 %

The correct answer is $\boxed{\text{B) 0.26\%}}$.

The effective gradient of a runway is the ratio of the change in elevation to the horizontal distance traveled. In this case, the change in elevation is 1.8 m, and the horizontal distance traveled is 1000 m. Therefore, the effective gradient is 0.018/1000 = 0.0018 = 0.26%.

Option A is incorrect because it is the change in elevation divided by the total length of the runway, not the horizontal distance traveled. Option C is incorrect because it is the change in elevation divided by the horizontal distance traveled, but the change in elevation is incorrect. Option D is incorrect because it is the change in elevation divided by the horizontal distance traveled, but the change in elevation is incorrect and the horizontal distance traveled is incorrect.