A sentence-ending particle used to question, confirm, or emphasize the preceding statement—often expressing surprise, challenge, or inquiry.
本当に行くのか。よく考えたほうがいい。
Are you really going? You should think it over.
そんなに簡単にあきらめるのか。
Are you going to give up that easily?
これで終わりなのか？
Is this the end?
A sentence-ending particle expressing lamentation or regret about the preceding matter; used to show disappointment or rueful reflection.
やはり彼は来なかったのか。寂しい。
So he really didn't come after all. How lonely.
あの時助けられなかったのか。今でも悔やんでいる。
So I couldn't help them back then. I still regret it.