What volume 12.6 m hcl must be added to enough water to prepare 5.00 litters of 3.00 m hcl?

To solve this problem, we shall use the role;
M1V1 = M2V2
M1: is the molarity of the solution before dilution.
V1: is the volume of the solution that we need to dilute.
M2: is the molarity of the solution after dilution.
V2: is the volume of the solution after dilution.

By substitution;
12*V1 = 3*5
V1 = 1.25 litters.

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.