Aqueous $Na X_{2} SO X_{4}$ is electrolysed between platinum electrodes. A few drops of litmus are present in the solution. Which observation is correct?

Answer: C

Neither

Na X^{+}

nor

SO X_{4} X^{2 -}

is discharged; water is electrolysed. Cathode:

2 H X_{2} O + 2 e X^{-} H X_{2} + 2 OH X^{-}

, so the region near the cathode becomes basic (blue). Anode:

2 H X_{2} O O X_{2} + 4 H X^{+} + 4 e X^{-}

, so the region near the anode becomes acidic (red). On mixing, the

H X^{+}

and

OH X^{-}

produced are equal in amount and the bulk pH is unchanged;

Na X_{2} SO X_{4}

only carries the current.