Asolution has a hydrogen ion (or hydronium ion) concentration of 1.00 × 10–9 m. what is the ph of the solution? 7.5 8.0 9.0 8.5

A solution that has hydrogen ion concentration higher than 10^-7 mol/L is acidic.
A solution that has hydrogen ion concentration lower than this is alkaline. 
pH is a measure of ion concentration. Solution with pH less than 7 are acidic, while those with pH higher than 7 are basic or alkaline. Solution with pH 7 are neutral solutions.
In our case , the hydrogen ion concentration is 1x10^-9 M, which is lower than 10^-7, so the solution is alkaline and its pH value is higher than 7. 
The pH can be calculated with the formula: pH=-log(H+)=-log(10^-9)=9

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