A2.00 g sample of a bromine oxide (brxoy) is converted to 2.94 g of agbr. all the bromine in the original oxide compound ends up in the agbr (molar mass for agbr = 187.8). determine the empirical formula of the bromine oxide.

In comparing two isotopes of the same element, the atomic number, stays the same.

Allow me to explain: The protons in an isotope ALWAYS stays the same, but the neutrons change. But, what's the atomic number made up of? 

Protons, which means it won't change. 

However, the atomic mass is made up of neutrons + protons, so only the atomic mass would change - not the atomic number.