Here's why:

* Azulene is a non-benzenoid aromatic hydrocarbon with the molecular formula C₁₀H₈.

* Empirical formula represents the simplest whole number ratio of atoms in a compound.

* To find the empirical formula, divide the subscripts in the molecular formula by their greatest common factor, which is 2 in this case.

* Therefore, the empirical formula of azulene is C₅H₄.