Since someone’s mother has four sons, North, West, and South, the name of the fourth son is someone.
The correct answer is ‘someone’. The question is a common riddle based on the mathematical topic called ‘sequences’. Thus, it calls that one neglects the use of logic as English requires.
Further Explanation
If one is to go by logic, logic will permit that one mentions east as the name of the fourth son. For one to have a better clarification of the question, background knowledge of what a sequence is must be buttressed with a typical example.
Although Sequence is an enumerated collection of objects in which repetitions of numbers are allowed, there can be puzzle-like questions in forms of riddles that are still under sequence.
Example: A man is sentenced to death; he has three choices to make among three rooms. The first room has plenty of raging fires. The second room has 5 assassins with loaded pump action rifles. The third room contains lions that have not been fed for 5 years. Which room will be the safest for the man?
Answer: The third room will be the safest mainly because the lions have not been fed for 5 years, which implies that they are dead.