In which chapter does Ralph begin giving up being the leader?William Golding's Lord of the Flies

Even as early as Chapter Six of Lord of the
Flies there are indications of the breakdown in leadership.  For instance,
after the beast has taken a physical form for the boys and become more real to
them, 

Ralph
took the conch from where it lay on the polished seat and held it to his lips; but then
he hesitated and did not blow.  He held the shell up instead and showed it to them and
they understood.

And, Piggy,
too, has his prominence and that of rationality symbolically diminshed as he "took off
his damaged glasses."   Jack challenges the use of the conch and Ralph's leadership as
he shouts "We don't need the conch!" but, after Ralph convinces the boys that the fire
is the most important thing, the boys rejoin Ralph's
side.

Then, in Chapter Seven, the sinister emergence of the
sadistic Roger threatens civilized behavior, and Jack becomes more dominant as Ralph
himself becomes involved in the hunt for the pig:

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"I hit him all right.  The spear stuck in.  I
wounded him."  He [Ralph] sunned himself in their new respect and felt that hunting was
good after all.

Jack leads
the group up the mountain in the next morning to find the pig that Ralph has hit.  Again
an "impervious Roger" appears and sits by Ralph, tapping the log on which they rest
after climbin the mountain.   Then, in Chapter Eight, Jack challenges Ralph's leadership
again, telling the boys that anyone who wants to hunt can come with him.  Finally, in
Chapter Nine, the contention between Jack and Ralph reaches its height as Jack and Ralph
argue about possession of the conch and the boundaries on authority.  Simon comes down
the mountain to tell the others that the beast is within them, but is killed, and Jack
steals Piggy's symbolic glasses.  For the most part Jack has control, but in Chapter
Eleven Ralph takes control one last time as he manfully reminds the others with him why
they need a rescue fire, leading them to try to regain
civilization. 

In this chapter, Jack and the others have
been liberated "into concealing paint."  Jack blows the conch and the boys congregate. 
However, with the savage killing of Piggy as Roger sadistically sends the pink granite
boulder careening down upon Piggy's head.  This is the climax of the novel, and the
point at which Ralph completely loses any leadership.