Different markets = different sellers, volumes, and prices.
Also, do check if each of those portals shows a clean-price or a dirty-price.
Yes.
One needs to initially link one’s Demat account on these portals during registration,
and will receive any purchased bonds in the demat account itself.
[ Source (NSE) ]
[ Source (BSE) ]
Yes, pledging is possible with securities held in one’s Demat account.
- Subject to the actual list of securities that can be pledged (and their respective haircut).
- Also, it apparently takes 1-2 months before a newly issued GSEC is allowed to be pledged.
The actual coupon-rate/yield of a bond being newly issued,
is determined by the initial competitive bidding for the bond.
In case you haven’t already, checkout this chapter on GSECs.