Kosi is the answer that matches the Bihar-specific fact asked in the question. The Kosi river is called the 'Sorrow of Bihar' because of its destructive flooding. It is one of the most flood-prone rivers in the world, changing its course frequently and causing widespread devastation in northern Bihar every year. The Kosi originates in Tibet and flows through Nepal before entering Bihar. Historically, floods from the Kosi have caused massive loss of life, displacement of people, and destruction of crops and property. The Ganga is the main river of Bihar but is not associated with sorrow. The Gandak is another major river but is not called the sorrow of Bihar. The Sone river flows through south Bihar and is known for its sandy bed. The Kosi disaster of 2008, when it breached an embankment in Nepal, was one of the worst floods in Bihar's recent history. Bihar GK questions frequently place neighbouring districts, rivers, historical centres, personalities or government institutions together as distractors, so recognition of a familiar name alone is insufficient. The alternatives Ganga, Gandak, Sone may be valid Bihar-related terms, but they do not satisfy the complete relationship asked here. Revise the complete pair ‘Which river is known as the 'Sorrow of Bihar'? — Kosi’ rather than an isolated option letter. This approach improves accuracy in BPSC, Bihar Police, teacher recruitment, SSC, Railway.
