Ionic bonds result from transfer of electrons, whereas covalent bonds are formed by sharing
Since HCl04 is a strong acid, being [H+], and a molarity of 2.1 M.
To solve for pH:
pH = -log (M) = -log(2.1M) = -0.32, which is clearly a negative number.
However, to verify the answer, just use the pH meter in determining the pH of the solution.