The pH of solution A is 2. The pH of solution B is 4. Which solution has the greater concentration of hydronium ions?
The concentration of that solution is how many times the
concentration of the other solution?

Solution A has the greater concentration of hydronium ions. That solution is 100 times more concentrated than the other solution.

Explanation:

For solution A take 10^-pH in this case 10^-2=.01

For solution B you would take 10^-4=.0001

.01>.0001 so solution A is more concentrated with H^+

To figure out how much more concentrated one solution is than the other:

(10^-2)/(10^-4)