pH is a scale which measures the acidity or alkalinity of a solution. It ranges from a level of 1 to 14. A pH which range from 1 to 6 represents an acidic substance. At pH of 7, signifies the solution is neutral. And at a pH of 8-14 represents a basic solution. pH is expressed as the negative logarithm of the concentration of hydronium ions.
pH = - log [H+]
Substituting pH and evaluating [H+]
9.55 = - log [H+]
10^-9.55 = 10^log [H+]
10^-9.55 = [H+]
[H+] = 2.82x10^-10 M or 0.000000000282 M
Therefore, the hydrogen ion concentration in a solution with a pH of 9.55 is 0.000000000282 M, option 3.