The sun is made mostly of ? helium nitrogen hydrogen argon oxygon

Sunis made of about 72 percent of hydrogen. The sun is also composed of about 26 percent helium and trace amounts of other elements — oxygen, carbon, neon, nitrogen, magnesium, iron and silicon.
so,if you want the element which made up MOST of sun than go for HYDROGEN. :)

You can tell that a chemical reaction occurred if there's bubbles, fumes and or evaporation. (: