As the ph approaches 0, what happens to the concentration of h3o+ ions?

We know that

pH = -log[H+]

the pH value falls in between 0- 7 for acids

As the pH value increases the concentration of [H+] increases.

similarly as the value of pH approaches 0, the concentration of H+ increases

The solution said to become more acidic

Also

[H+] X [OH-] = 10^-14

Thus pH + pOH = 14

hence the concentration of OH- decreases as the pH approaches zero