oh.. it seem like a kind of quizs for native korean kids.
the counting word for 젓가락 is '쌍'
젓가락 한 쌍 두 쌍 세 쌍
but we hardly use this word.
we say simply '젓가락 한 개 두개 세 개'
here is a fun story about this happening to me.
i was in a chicken store to take out a fried chicken
and there was a couple who ordered some chikens.
The cleark asked to them 'how many chopstics do you need'
and then the man of the couple answered "We need 여섯개"
After a while he corrected his words into "세개"
and then the girl of the couple started laughing and said "you idiot! you thought 젓가락 한 쌍 is actually 두 짝 and just multiplied 3 by 2"
and then all the people in the store laughed.
By the way, a half of 젓가락 한 쌍 is called 젓가락 한 짝