Step 1: Identify the core question. The question requires classifying the Harmonium by its sound production method.
Step 2: Analyze the mechanism. The Harmonium generates sound through air, propelled by bellows, vibrating metallic reeds. This air-driven sound production categorizes it as a wind instrument. In Indian musicology, it's a 'Sushira Vadya' and a 'free-reed aerophone'. Other instrument types, like string ('Tata Vadya' - Sitar), percussion ('Avanaddha Vadya' - Tabla), and metallic percussion ('Ghana Vadya' - Manjira), operate differently.
Step 3: State the classification. The Harmonium is classified as a Wind Instrument.