The element that is a nonmetal, a gas, and has an element symbol that starts with the letter a is Ar (Argon).
Element Ar (Argon) is the third member of noble gases, in period 8, and makes up about 1% of the Earth's atmosphere. It has approximately the same solubility as oxygen and it is 2.5 times as soluble in water as nitrogen. It is an inert element that is colorless and odorless in both its liquid and gaseous forms.