Incorrect formula for Hydronium ion is:

The correct formula for Hydronium ion is ${\mathrm{H}}_3{\mathrm{O}}^{+}$. 

${\mathrm{H}}^{+}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{H}}_3{\mathrm{O}}^{+}$

The following are a few of the general characteristics of acids:-

While the red litmus paper is unharmed, they turn the blue litmus paper red.
They cause the solution medium to emit hydrogen ions, which mix with water to generate hydronium ions.

Hence, option D is correct.