In chapter 10 among the hidden what happens?

That night at dinner, Luke's mom is showing off the bread that he made earlier.  Taking a chance, Luke asks if they could draw the shades and have him sit at the table.  Mr. Garner doesn't go for that, but understandably: someone might see his shadow. Can't blame Luke for trying, right?  When Mark says "Yuck" in response to learning that Luke made the bread, Luke comes back and replies that he poisoned it to only affect 14-year-olds.  Sure, it's a joke, but it makes Luke think: if something ever happened to one of his brothers, could he be the 2nd child? (We have to give this kid credit for thinking outside the box.)  Obviously he can't ask that but it's a good question nonetheless.  Turns out the bread doesn't taste that good. Mr. Garner says it's no big deal since "That's what a man gets married for". Uh … okay, Mr. Gender Roles. How about "That's what a man goes to the grocery store for?". Time to play Round Two of Jokes That Make Luke Think. While Matt and Mark tease Luke about getting married and Luke saying he won't invite them, Luke recognizes that he won't ever get married since he won't ever leave the house. Kind hard to meet girls when you live in an attic. Shortly after that, Luke excuses himself from dinner (which he is never the first to do). Back in the attic he stares out of the vent. He can easily see lights on in the neighboring houses. And even some shadows, too. Except for the Sports Family. Their blinds didn't let any light out nor any peeping eyes to see in. Curious and curiouser.

your answer is c) experiments with water vapor showed that elements combine in specific proportions.