Chose the correct relative pronouns in accordance with the sentence

The neighbour ___ son is always running around the street is a fireman.

The correct answer is: Whose

The correct answer is "Whose".
Here, we get two distinct sentence segments, namely "The neighbor is a fireman", and "The fireman's son is always running around the street". "The fireman" is the common portion which must be substituted for a relative pronoun to link the two parts. Among the given options, "Whose" is the most suitable alternative to show ownership of something or relationship with someone (here, the fireman's son). So, the correct answer is "Whose".