Morchang is –

Why the description 'a non-membranous percussion instrument' is incorrect: That category refers to solid objects that produce sound when struck; the morchang's primary sound mechanism is mouth resonance rather than the body being struck.

Why the description 'a plucked stringed instrument' is incorrect: Plucked string instruments create sound from vibrating stretched strings; the morchang has no strings and does not rely on that mechanism.

Why the description 'a percussion instrument' is incorrect: General percussion instruments are sounded by being struck or by vibrating membranes; the morchang's sound comes from a vibrating element resonated by the mouth rather than by striking a membrane or body.