If the amount of atoms of each type on the left and right sides of a reaction differs, what must be done to balance it?

a. coefficients are placed in front of the reactants and/or products

b. subscripts are placed in the chemical formulas

c. it should be left alone

d. superscripts are placed in the chemical formulas

Answer: option a. coefficientes are placed in front of the reactants and / or products

For example:

H2 + O2 - - > H2O

In the left side there are 2 atoms of oxygen and in the right side there is 1 atom of the same element.

Then you must put a number 2 in front of the product with this result:

H2 + O2 - - > 2H2O

Now there in the left side there are 2 atoms of hydrogen while in the right side there are 4 atoms of the same element. Then you have to put a 2 in front of H2 in the left side, with this result:

2H2 + O2 - - > 2H2O

Now the number of hydrogen and the number of oxygen atoms in both sides are equal, i. e. the equation is balanced.