What range of $pH$ is considered perfect for a fertile land?

What is the $pH$ value of a basic aqueous solution?

The $pH$ of a water sample collected from a river was found to be acidic in the range of $3.5 - 4.5$. On the banks of the river were several factories that were discharging effluents into the river. The effluents of which one of the following factories is the most likely cause for lowering the $pH$ of river water?

In a basic aqueous solution,what happens to the basicity of the solution as the concentration of $[OH^-]$ increases?

If the concentration of hydronium ions in an aqueous solution is $[H_3O^+] = 10^{-5} \; M$,what is the $pOH$ of the solution?

The $pH$ range most conducive for the life of freshwater plants and animals is: