Meaning of trailing の in a question


I've been running into this trailing の particle quite often and can't seem to
understand what exactly it means. Is it replacing か, or does it mean something
else?

For example:

> まだ生{い}きているの？




"Instead of 「か」, real questions in casual speech are usually asked with the
explanatory の particle or nothing at all except for a rise in intonation"

<http://www.guidetojapanese.org/learn/grammar/question>




"Instead of 「か」, real questions in casual speech are usually asked with the
explanatory の particle or nothing at all except for a rise in intonation"

<http://www.guidetojapanese.org/learn/grammar/question>

