题目

One day a boy was walking along the street. Suddenly he stopped and looked up into the sky.A young man passed by him. When he saw the boy, he felt curious and looked up, too.Just then a girl came up and saw them. “Is there anything interesting in the sky?” She thought and looked up, too.After a while there were quite some people. They were interested in the clear blue sky.Suddenly the boy asked, “Hey, what are all of you looking up at?” “That’s what we are going to ask you,” said the young man. “You want to ask me? But I wasn’t looking at anything,” said the boy. “I raise13．实验小组探究盐酸和氢氧化钠反应过程中溶液pH的变化规律，得到如图所示曲线．（1）B点表示的意义是盐酸与氢氧化钠恰好完全反应或pH═7或溶质是NaCl．（2）当溶液的pH为C点时，溶液中的溶质是NaCl、HCl．（填化学式）