Which river of Bihar has traditionally been called the Sorrow of Bihar?

The correct answer is B, the Kosi. The Kosi comes down from Nepal carrying an enormous load of silt, drops it on the flat plain and so keeps raising its own bed. Over the last two centuries the river shifted its channel many kilometres westward, abandoning old courses and flooding fresh country each time, which cost lives and land and earned it the name Sorrow of Bihar. The barrage at Bhimnagar and the embankments were the response.

Option A, the Gandak, also floods but is controlled by the Valmiki Nagar barrage and does not wander in the same way. Option C, the Sone, is a south bank river with a rocky bed that is used for irrigation rather than feared for floods. Option D, the Punpun, is a small south Bihar river that can flood Patna locally but carries no such name. Note the parallel nicknames asked with this one, the Damodar as the Sorrow of Bengal and the Hwang Ho as the Sorrow of China.