How can hydrogen and oxygen be made to combine chemically to form water?
Any flame or electric spark will trigger this explosive reaction!
Yes indeed you can combine oxygen and hydrogen chemically to form water, simply by burning hydrogen in oxygen or air - two atoms of hydrogen combine with one atom of oxygen to form H2O - (although strictly speaking, in the context of chemistry, the water so produced would not necessarily be a "mixture").
Almost any element can be in a molecule. Carbon and hydrogen can chemically combine to form hundreds, if not thousands, of different hydrocarbons like methane, propane, and butane. Hydrogen and oxygen can combine to form water and hydrogen peroxide. Carbon and oxygen can combine to form carbon dioxide and carbon monoxide.