Balance FeCl3 + MgO ---> Fe2O3 + MgCl2

The balanced equation is

Explanation:

The given reaction equation is as follows.

Here, number of atoms present on reactant side are as follows.

Number of atoms on product side are as follows.

To balance this equation, multiply by 2 and MgO by 3 on reactant side. Also, multiply by 3 on product side. Therefore, the equation can be rewritten as follows.

Hence, number of atoms on reactant side are as follows.

Number of atoms on product side are as follows.

Since, this equation contains same number of atoms on both reactant and product side. Therefore, this equation is now balanced equation.

Thus, we can conclude that the balanced equation is .

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.