Alexander and Porus fought a battle at Hydaspes. The Battle of Hydaspes took place in 326 BC between the Macedonian king, Alexander the Great, and the Indian king, Porus. The battle was fought near the river Jhelum, which is located in present-day Pakistan. Option 1, Hydaspes, is the correct answer as it accurately represents the actual battle location. However, it is worth noting that the river Jhelum is also known as the Hydaspes River, which might cause some confusion. The other options, Panipat and Tarain, refer to different battles fought in India but did not involve Alexander the Great. Therefore, option 1, Hydaspes, is the correct choice.