What is the passing score for developer plus exam?
62%, according to the link you have given.
Which study materials useful for preparation of this exam except Free study Guide?
There are none yet. Only very few people have passed the exam. For some additional information, see my blog post.
What is the retake policy for this exam?
From the Email I received after failing the exam:
You will be required to wait for a period of at least seven (7) calendar days from the date of your last attempt before you are allowed to retake the exam. For subsequent failed attempts you will be required to wait 14 days for the third attempt, 21 days for the fourth attempt and 30 days for the fifth attempt from the date of your last attempt.
I hope that answers that.
How many free retakes are available?
None. You will receive a 20% discount though.