Q1.
You will find small droplets of water inside the boiling tube near its open end. Where did this water come from? Was it in the dry sugar, or did it come by the condensation of water vapour in the air?
Answer
The water came from the dry sugar itself, not from the air.
Why we can be sure: We are heating the tube. Water vapour from the air condenses on a cool surface, never on a hot one — so nothing from the air could settle inside a boiling tube that is being warmed. The droplets appear near the open end, the coolest part of the tube, exactly where a vapour coming from inside would cool and condense. And the sugar we started with was dry.
So heating has broken the sugar down, and one of the products is water. Since water itself consists of hydrogen and oxygen, the sugar must have contained hydrogen and oxygen — sugar cannot be an element.