Explanation:

Ganga enters the boundary of Bihar at Chausa a village near Buxar after its confluence with Karmanasa.
The Bihar plain is divided into two unequal halves by the river Ganga which flows through the middle from west to east.
The most common soil in Bihar is Gangetic alluvium of the Indo-Gangetic plain region Ganga river originates as Bhagirathi from the Gangotri glacier.
• Alaknanda river joins Bhagirathi at Devprayag, onwards known as Ganga.
• It is joined by the river Yamuna at Allahabad.
• At Farraka, it bifurcates into Bhagirathi-Hugli in West Bengal and Padma - Meghna in Bangladesh.
• It drains into the Bay of Bengal.
• Tributaries- Yamuna, Gandak, Ramganga, Son, Ghaghra, Gomti, Kosi, Tamsa, Punpun, and Mahananda.