In the chemical formula for an ionic compound, which item is written first?
a. positive ion
b. negative ion
c. subscript
d. charge

a. Positive ion

Explanation:

An ionic compound is formed by a metal and a nonmetal, or metal and hydrogen. The metal will donate electrons and will be a cation (a positive ion), and the nonmetal or the hydrogen will gain electrons and will become an anion (a negative ion).

In the chemical formula, first comes the cation, and then the anion, with their charges changed, without the signal. For example, to form the compound between sodium (Na) and chlorine. Sodium is from group 1, and it must donate 1 electron; chlorine is from group 7 and it must gain 1 electron to be stable, so the ions are:

Na⁺ Cl⁻, and the compound NaCl.

if you mean hydrogen and oxygen then water is the product

it means there are 3 atoms of oxygen