The process in which the concentration of the solution is lessened by the addition of water is said to be dilution and equation of dilution relates the initial concentration and volume of stock solution with the final concentration and volume of the solution.
Formula is given by:
[tex]C_{1}V_{1}=C_{2}V_{2}[/tex] (1)
where,
[tex]C_{1}[/tex] is the initial concentration
[tex]V_{1}[/tex] is the initial volume
[tex]C_{2}[/tex] is the final concentration
[tex]V_{2}[/tex] is the final volume
Now,
[tex]C_{1}[/tex] = 0.850 M
[tex]V_{1}[/tex] = 4.12 L
[tex]C_{2}[/tex] =?
[tex]V_{2}[/tex] = 10.00 L
Substitute the give values in formula (1),
[tex]0.850 M\times 4.12L=C_{2}\times 10.00 L[/tex]
[tex]C_{2} =\frac{0.850 M\times 4.12L}{10.00 L}[/tex]
= [tex]0.3502 M[/tex]
Thus, the final concentration of the[tex]H_{3}PO_{4}[/tex] solution = [tex]0.3502 M[/tex]