Which of the following pairs is not correctly matched with respect to south of…

The Ganga river divides Bihar into two distinct geographical regions: North Bihar and South Bihar. To be a "correctly matched" pair with respect to the south of Ganga region, both districts in the pair must be located south of the river.

• Patna is located on the south bank of the Ganga.

• Vaishali is located on the north bank of the Ganga.

• Because this pair contains one district from the south and one from the north, it is not correctly matched for a region strictly defined as "south of Ganga".