Yes because color change is a sign of a chemical reaction.
When a gas bubbles through water, small droplets of water are usually picked up along for the ride and are mixed in with the gas above the water inside the eudiometer tube. The water vapor takes up room, but isn't the important gas that you need to measure. The table of water vapor is needed to subtract the unwanted water vapor from the collection of gases.
A. hydroxide is the answer
No, within a crystal like structure or ionic lattice of sodium chloride, there are ions of Na and Cl. Na+ and Cl- respectively that are attracted to each other due to their opposite charges. Many of these ions form a crystal structure.
