Question

What is the chemical formula of a compound that is composed of the ions Camc007-1.jpg and Brmc007-2.jpg?

Answer 1

The option that qualifies as a chemical formula of Ca2 and Br- would be CaBr2, the second option.

Answer 2

Calcium ions have oxidation state 2+ => Ca (2+).

Bromime ions (bromide) have oxidation state 1- => Br (-).

So, to be neutral the compound has to have two Br (-) ions per each Ca(2+) ion.

That is represented in the chemical formula as Ca Br2, where the number 2 to the right of Br is a subscript meaning that there are two atoms of Br per each atom of Ca (the lack of subscript means 1 atom).

Answer: Ca Br2.