Explanation:

- Ustad Bismillah Khan was a legendary Indian musician known for his prowess on the shehnai.

- Option 1: Santoor – This is a different stringed instrument, mainly played with mallets, and is not associated with Bismillah Khan.

- Option 2: Sitar – This is a plucked string instrument used in Hindustani classical music, famously played by artists like Ravi Shankar, not Bismillah Khan.

- Option 3: Shehnai – A traditional Indian wind instrument akin to an oboe, and the one Bismillah Khan was renowned for playing, bringing its music to the global stage.

- Option 4: Tabla – This is a percussion instrument, played with hands, and is not related to Bismillah Khan's legacy.