This answer would be heat capacity
A) number of neutrons in the nucleus... all isotopes of an element contain the same number of protons which is equal to that elements atomic number...
hope this helps!
Barium :

with +2 being the charge
Oxygen :

with -2 being the charge
The given equation can be written as:
Ba + O = BaO
Since the sum charges of Barium and Oxygen equals 0, there is no need to add subscripts.
Both Ba and O appear on the left and right side of the equation once, so there is no need to add a coefficient.
Ba + O = BaO is balanced
The subscript 2 indicate that there are two atoms of chlorine in the compound.
<u><em> Explanation</em></u>
Subscript in the chemical formula indicate the number of atoms of the element immediately before the subscript.
In MgCl₂ there are two(2) atoms of chlorine since Subscript 2 is immediately after chlorine.