We are given the following directions:
1. Mr. X's house faces East, so the front door is facing East.
2. He walks 50 m straight from the back door, which is opposite the front door, so he is walking in the West direction.
3. After reaching the end of the 50 m, Mr. X turns to his right, which would be the North direction.
4. He then walks 50 m North.
Now, the direction of the point Mr. X is located at, with respect to his starting point, is in the North-West direction.
Thus, the correct answer is North-West.
Final Answer: (D)