What is pH of a 1 molar solution of an acid that has a Ka - 10.8?

None of these

For a strong acid with a high $K_a$ value (10.8), it fully ionizes in water.

pH is calculated as $pH = -log[H^+]$ , and for a 1 M strong acid, $[H^+] = 10^{-4}$ , so pH = 4.