meaning - When is -の used for a question

When is -の used for a question and what is the exact meaning

Context:

(nj) = (Native Japanese speaker)

• (njs): 学校に行くの?


• (me): いいえ、学校は行きません。


• (njs): 自分でやるの？


• (me): 自分やります。

Answer

の is a more casual/friendly way to ask a question when ですか or Vますか would feel a little bit too polite. You can think of it as ん(の)ですか without the ですか part. For instance:

学校に行きますか？ 学校に行くの？

These sentences have the exact same meaning but the first one is much more formal. Note that 学校に行くか is a bit harsher and more rarely used.

Also, Nounですか becomes Nounなの？ You need the な otherwise it means "the one of [Noun]?". You will also need the な if you are connecting a な-adjective.

簡単ですか。 簡単なの？