The correct answer is option 4, Muhammad bin Qasim. Muhammad bin Qasim was the Commander of the Arab army who conquered Sindh. He was a young general from the Umayyad Caliphate who led the military campaign in the early 8th century. Muhammad bin Qasim`s conquest of Sindh was part of the larger Arab conquest of the Indian subcontinent. He led a well-organized and disciplined army that successfully defeated the ruling Hindu dynasty in Sindh. Muhammad bin Qasim`s conquest had significant consequences for the region, as it introduced Islam to the Indian subcontinent and established Arab rule in Sindh for several centuries. It is important to note that AlHazzaz, Qutbuddin Aibak, and Allauddin Khilji are not related to the conquest of Sindh.