Asolution has a hydrogen ion (or hydronium ion) concentration of 3.16 x 10^-9m. what is the ph of the solution

PH value is a numeric scale used to indicate the acidity or basicity of an aqueous solution. The calculation of pH value is pH = -log[H3O+]. [H3O+] is the concentration of hydrogen ion (or hydronium ion) in the solution, in the unit of mole/L (or M).  Given that the concentration of hydronium ion is [H3O+]=3.16x10-9M, therefore pH of this solution is pH = -log(3.16x10-9) = -(-8.5) = 8.5.  pH value is larger than 7, so this solution is basic.

What are the options? physical property can be color, smell, opacity, viscosity, density, infra red spectrum, melting and boiling points, attraction and repulson to magnets, etc.

A)  it is neutral because the concentration of hydronium ions equals that of hydroxide ions