Intentional grounding

[BoBo]

I know we have been down this road before but please refresh my mind.

4th Down and 10 from A's 20 yard line.

A1 (QB) drops back to the A's 10 yard line, in the process of being tackled intentionally grounds the ball where nobody but inelgibles stand.

Question 1:
Throw the flag at the spot of the foul= A's 10 yard line
This I know is true.

Question 2:
What are B's options:
A) If they accept the penalty where is the 5 yards marked of from and what and whose ball is it?

B) If declined where and whose ball is it?

We always get confused because one of the fundamentals is "No foul can result in the change of possession"

Any comments appreciated.