Answer:
3. There are no rules from grown-ups
Explanation:
According to the Chapter Four of Golding's Lord of the Flies, the boys are happy because there is no rules for grown-ups.
As they have been trapped on the island for some time and have to cater for themselves, they quickly organize themselves, elect a leader and begin to learn how to survive.
In Chapter Four, after the killing of the pig, the boys are happy at their independence and freedom from rules of grown-ups.