It is important to realise that for a group be pass-alive (i.e. uncapturable even if the attacker is allowed to make as many moves as they want), each chain belonging to the group has to have two โchain-eyesโ within the group. See Benson's Definition of Unconditional Life at Sensei's Library or the summary of it at Formal Definitions of Eye at Sensei's Library.
This is what is necessary to ensure the attacker cannot pick the group apart one chain at a time: to capture any chain, they would have to play in both its eyes.
A โpass-aliveโ group may be thought of one where the fight has been completely played out, by the attacker playing as many threats as possible, and the defender answering each, until it can no longer even be threatened.
I donโt like this definition because of the confusion the word โthreatโ can cause.
In go, this word is most often associated with ko threats.
However, a group might not be pass-alive even though there are no immediate ko threats against it.
There is no ko threat against this black group. The black group is not pass-alive, but in order to capture it, White needs to play 4 moves in a row, and the first two moves are not threats.
Let not get too deeply in an answer to someone discovering the game.
Not the place to start debating on pass-alive, threats, sekis, and more. Really not what is expected as an answer.
