Neutral pH means a pH of 7, yes? Recall that 'pH' means the POWER of Hydrogen. You should be familiar with the equation : pH = -log[H+].
In this case, 7 = log[H+].
Mathematically rearranged, this means that to find H+ concentration,
[H+] = 10 ^-pH.
In this case, [H+] = 10 ^-7.
I am assuming this is conducted at a standard 25 degrees. The auto-dissociation formula of water is this: Kw = [H3O+] x [OH-] at 25 degrees.
The concentration of Hydronium is the same as the concentration of hydrogen, 10 ^-7. mol/L.
There's your answer!
