How many times greater is the hydronium ion concentration in rainfall (pH = 5.0) compared to pure water (pH = 7.0) ?

a.) 100 times

b.) 1 time

c.) 1000 times

Hydronium ion is H3O (+)

pH is log 1 / [H3O (+) ] = - log [H3O (+) ]

Rainfall: pH = 5.0 = - log [H3O (+) ] = > [H3O (+) ] = - antilog ( - 5.0) = 10^-5

Water; pH = 7.0 = - log [H3O (+) ] = > [H3O (+) ] = - antilog (-7.0) = 10^ - 7

Divide hidronium conentration of rainfall by hidrodium concentration of water:

10^-5 / 10^-7 = 10^2 = 100.

Then, hidronium concentration in rainfall is 100 times hidronium concentration in water.

Answer: option a. 100 times.