The correct sequence of Himalayan rivers joining the Ganga downstream of Prayagraj from West to East is Gomati, Ghaghara, Gandak, and Kosi. This order is significant geographically, as it reflects the hydrology of the region: the Gomati flows from the west, while the Ghaghara and Gandak, which originate in the Himalayas, join the Ganga subsequently from the north-northwest before the Kosi, which has a more eastern course. Understanding the arrangement of these tributaries is crucial in grasping the river basin dynamics and sediment transport processes that support agriculture and livelihood in the fertile Gangetic plains, which is essential knowledge for the UPSC examination context.