Yung is not the possesive pronoun iyong (your). Yung is a replacement for ang. In heavy Tagalog conversations, you'll find that ang is being replaced by yung.
Yun is also the same as yung. Yung is actually yun plus the final ligature -g. But it depends on the context because yun can be iyon(used to refer to an object or place not close to the speaker or the person he is speaking to).
A. Nakita mo ba ang bolpen ko? = Nakita mo ba yung bolpen ko? = Have you seen my ballpoint pen?
B. Yun ba ang bolpen mo? = Yun ba yung bolpen mo? = Is that the ballpen (you were talking about)? -> said while pointing to the ballpoint pen which is far from the speaker and the listener.
In this particular sample conversation, yun is iyon(can be translated to 'that') and yung pertains to a specific object, the ballpen which the speaker is talking about.
Ang can be used but yung will best identify the object which was mentioned.
BINABASA MO ANG
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