I learned over the course of public speaking that asking questions to an audience is both a great way to engage them, but also a minefield of risks. The rule I now use is "Ask questions everyone can answer."
A couple of real-life examples while engaging a grade school class.
I asked the question "Do you know how Gorilla glass was invented?", and every student knew the answer and the whole room responded "No." If I had asked "How was Gorilla glass invented?", which is unlikely anyone would know, the response would have been uncomfortable silence. Children, and adults, don't like being stupid and will disengage, at least a little, and maybe a lot. What I found interesting was every student listened to exactly what I said. When I repeat that to adults they tend to ignore the "Do you know" part.
I then explained how the glass the scientists were working on was accidentally heated way beyond what they intended. Then I asked "When they took the cooled-down glass out of the heater, they dropped it on a hard floor. What do you think happened then?" Every student shouted out "It shattered!!" And I shouted back "No, it bounced!" and the entire class broke into laughter. The fact everyone got the wrong answer was terribly funny to them. No one felt left out or felt less of themselves.
I've asked other questions that I wish I had thought more about before the words came out. But I would instantly know from the looks on some of the people's faces I had made them feel bad. I would think about why that particular question was phrased poorly and restructure it for the next time. For example, I asked that same class above "Who has a cell phone?" Most hands shot up, but not all, and I could tell by the faces of the few hands-down students I made them feel like outcasts. I changed that question to "Who has an iPhone?", talked about that, and then asked "Who has an Android phone?" a few minutes later. The students without cell phones could keep their hands down for both questions, but there were lots of other hands down at the same time, keeping them out of an embarrassing situation.
