The correct answer is (a). The elevation of Punjab generally decreases from northeast to southwest. This is because the region is located in the foothills of the Himalayas, which are a mountain range that runs from northeast to southwest. The higher elevations of the Himalayas are located in the northeast, while the lower elevations are located in the southwest.
Option (b) is incorrect because the elevation of Punjab does not increase from northeast to southwest. The elevation of the region decreases from northeast to southwest.
Option (c) is incorrect because the elevation of Punjab does not decrease from east to west. The elevation of the region decreases from northeast to southwest.
Option (d) is incorrect because the elevation of Punjab does not increase from north to south. The elevation of the region decreases from northeast to southwest.