The Ghaghara River mainly joins the Ganga in the plains of which state?

Correct answer: Bihar

The governing concept is the drainage relationship between a tributary and its main river. The Ghaghara, known as the Karnali in its upper Himalayan course, enters the northern plains and flows through the Uttar Pradesh region before joining the Ganga near Chhapra in Bihar. Thus Bihar is the appropriate answer, and option A is correct. Kerala and Maharashtra are peninsular states with different drainage systems, while Rajasthan lies outside the Ghaghara’s route. The question is not asking where the river rises or which state it first enters; it asks where its important confluence with the Ganga occurs. Tracing the river downstream to its meeting point with the Ganga distinguishes Bihar from the plausible but geographically unrelated alternatives.