Correct option is A
Given:
I is J's maternal uncle → (I is J's mother’s brother.)
I is K's son → (K is I's parent.)
I is M's only sibling → (M and I are siblings.)
I is L's father → (L is I’s child.)
I is N's nephew → (N is I’s uncle/aunt.)
I is K's son → (K is I's parent.)
I is M's only sibling → (M and I are siblings.)
I is L's father → (L is I’s child.)
I is N's nephew → (N is I’s uncle/aunt.)

According to the given information,family tree diagram will be:

As per the diagram, M is the only sibling of I, so M is J's mother.
Thus, the correct option is (a) Mother