In Chapter 7, what does Ralph sense about Jack after Ralph asks him about the pig run? What does this tell him about Jack?

“Wait a minute though! Where does the pig-run go to?”

“The mountain,” said Jack, “I told you.” He sneered. “Don’t you want to go to the mountain?”

Ralph sighed, sensing the rising antagonism, understanding that this was how Jack felt as soon as he ceased to lead.

There's the bit of the novel you need. Ralph is sensing the "rising antagonism" - that is, Jack's growing unwillingness for Ralph to be chief, and Jack's growing desire to lead himself. "... this was how Jack felt as soon as he ceased to lead". It's an early indicator from Golding that Jack not only resents Ralph, but already has thoughts of being in charge himself. And though Ralph recognises it, he doesn't act decisively enough to prevent the inevitable: Jack challenging his authority on the island.