Identify from following an example of Lewis acid.

A Lewis acid is a chemical species that can accept a pair of electrons.

In boron trifluoride ($\text{BF}_3$), the central boron atom has only six electrons in its valence shell, making it an electron-deficient molecule.

Due to this incomplete octet, $\text{BF}_3$ can accept an electron pair to complete its octet, thus acting as a Lewis acid.

$\text{H}_2\text{SO}_4$, $\text{HClO}_4$, and $\text{CH}_3\text{COOH}$ are Bronsted-Lowry acids as they donate protons ($\text{H}^+$).

Answer: $\text{BF}_3$