This is the 811th most frequent Japanese word.
なか
"なか" (naka): inside; middle; among.
Here, 'なか' is used to indicate the interior of a location, specifically the inside of the house.
家のなかはとても静かだった。
It was very quiet inside the house.
In this instance, 'なか' metaphorically represents the individual's inner thoughts or mind.
どちらが好きか自分のなかで考えた。
I thought about which I liked within myself.
In this sentence, 'なか' refers to the contents or elements within his story, essentially meaning 'inside' or 'within the scope of'.