Answer: A.
B.
C.
Thus solution B is basic in nature.
Explanation:
pH is the measure of acidity or alkalinity of a solution.
pH is calculated by taking negative logarithm of hydrogen ion concentration.
pH for acidic solutions is less than 7, for basic solutions it is more than 7 and for neutral solutions it is equal to 7.
![pH=-\log [H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%20%5BH%5E%2B%5D)
![pOH=-log[OH^-]](https://tex.z-dn.net/?f=pOH%3D-log%5BOH%5E-%5D)

or ![[H^+][OH^-]=10^{-14}](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%5BOH%5E-%5D%3D10%5E%7B-14%7D)
A.
![pH=-log[H_3O^+]=-log[0.64\times 10^{-7}]=7](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D%3D-log%5B0.64%5Ctimes%2010%5E%7B-7%7D%5D%3D7)
B.
![pH=-log[H_3O^+]=-log[9.43\times 10^{-9}]=8](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D%3D-log%5B9.43%5Ctimes%2010%5E%7B-9%7D%5D%3D8)
C.
![pH=-log[H_3O^+]=-log[0.000775]=3](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D%3D-log%5B0.000775%5D%3D3)
Thus solution B is basic.
May i ask you what lesson this is ?
Low air pressure cause it was on my test last year