Two loads of 50 kg and 75 kg are hung at the ends of a rope passing over a smooth pulley shown in below figure. The tension in the string is: A. 50 kg B. 75 kg C. 25 kg D. 60 kg

The correct answer is $\boxed{\text{D}}$.

The tension in the string is the same on both sides of the pulley. This is because the pulley is smooth, so there is no friction. The forces acting on each mass are the weight of the mass and the tension in the string. The weight of the 50 kg mass is 50 N, and the weight of the 75 kg mass is 75 N. The tension in the string must be equal to the sum of the weights of the two masses, or 125 N.

Option A is incorrect because the tension in the string is not equal to the weight of the 50 kg mass. Option B is incorrect because the tension in the string is not equal to the weight of the 75 kg mass. Option C is incorrect because the tension in the string is not equal to half the sum of the weights of the two masses.