Pre/Post gaps


I am trying to better understand the structuring of sector blocks in a CDrom.
That leads me to ask questions.
I know that in this forum, there are eminent specialists who could “enlighten” me.
Thank you for your help.

Post Gap :

I have difficulty defining what a post gap is.
Obviously this is a set of a minimum of 150 sectors.
It is at the end of a track.
Then I have conflicting definitions.
One says that the post gap is contained in a separate index.

[index 01][index 02]

The other says that the post gap immediately follows the track data.

[index 01 (post gap)]

I would like a clarification of what the Red book /Yellow Book standard says.

Lead Out Transition :

I did not find information on what kind of transition is between
the last track of a session and the lead out.

[last track (audio)] [?] [Lead out]
[last track (data)] [?] [Lead out]

Mode 1 or 2 track to Audio track transition :

I read in ECMA 394 (13-17) :
“No Pre-gap, start Track with 2 seconds digital silence”
Is that 2 seconds merge with index 01 of audio track or is it encapsulated in an Index 00 ?