Identify the type of defect in brass alloy.

Brass alloy contains zinc atoms substituting copper atoms in the lattice structure. This creates a substitutional impurity defect, defined by impurity atoms occupying regular lattice sites.

Interstitial defects involve smaller atoms fitting between lattice positions, while Schottky defects require ionic crystals with cation/anion vacancies. Metal deficiency defects occur in non-stoichiometric compounds with variable oxidation states.

Zinc's atomic radius ($134\,\text{pm}$ vs copper's $128\,\text{pm}$) allows direct substitution without significant lattice distortion, confirming the substitutional nature.