Nitrogen is crucial to the marine life and it is disappearing because it cannot be assimilated by most organisms in the water.
Answer:
Option a is a solution acidic ([OH⁻] = 7.0x10⁻⁹ M).
Explanation:
To know if a solution is acidic we need to calculate the pH and it must be lower than 7. A value of pH equal to 7 is a neutral solution and a solution with a pH value higher than 7 is a basic solution.
a. For the [OH⁻] = 7.0x10⁻⁹ M we have:
![pOH = -log[OH^{-}] = -log(7.0 \cdot 10^{-9}) = 8.15](https://tex.z-dn.net/?f=%20pOH%20%3D%20-log%5BOH%5E%7B-%7D%5D%20%3D%20-log%287.0%20%5Ccdot%2010%5E%7B-9%7D%29%20%3D%208.15%20)
Now, the pH is:


This solution is acidic (pH < 7)
b. [H₃O⁺] = 8.5x10⁻⁸ M

This is not an acidic solution. Is a neutral one (pH around to 7).
c. [OH⁻] = 2.5x10⁻⁶ M
![pOH = -log[OH^{-}] = -log(2.5 \cdot 10^{-6}) = 5.60](https://tex.z-dn.net/?f=%20pOH%20%3D%20-log%5BOH%5E%7B-%7D%5D%20%3D%20-log%282.5%20%5Ccdot%2010%5E%7B-6%7D%29%20%3D%205.60%20)
Then, the pH is:

Hence, this is not an acidic solution. It is basic (pH > 7).
Therefore, option a is a solution acidic ([OH⁻] = 7.0x10⁻⁹ M).
I hope it helps you!