The concentration of hydronium ions is greater than 1x10-7 for basic solutions

FALSE

Concentration (M)= mol of substance/ given liter

OH- is hydroxide, a BASE
> proton acceptor
> produce hydroxide ions when dissolved in solution
H3O+ is hydronium, an ACID
> proton (H+) donor
> produce hydrogen ions when dissolved in solution

For more BASIC solutions:
concentration of BASE> con. of ACID
con. OH- > con. H3O+

The concentration of H3O+ must be less than or SMALLER than 1x10^-7 (so 1x10^-8, 1x10^-9 etc.) whereas the concentration of the base, OH-, must be LARGER than 1x10^-7. So there is a higher concentration of OH-, or more mol OH per L of solution.

pH measure the concentration of H+ or H3O+ ions in solution. It is -log[H+] ... so if the concentration was lower than 1x10^-7 mol/ L
-log(1x10^-8)= pH= 8 which is Basic (x>7)

Remember, for the pH scale,
(0-7)= acidic
7= neutral
(7-14)= basic

Conversely, for acidic solutions, the concentration of hydronium would increase

The correct answer is b

I'm not sure but i will try to find out