The correct answer is Pataliputra.

Chandragupta Maurya, the founder of the Maurya Empire, established Pataliputra as his capital. Pataliputra, located in modern-day Patna, Bihar, India, was strategically chosen for its location on the Ganges River, making it a vital center for trade and commerce. Its central location also facilitated the efficient administration and control of the vast empire.

While Magadha was a region and the core of the early Maurya empire, Pataliputra was specifically the *capital city* established by Chandragupta Maurya. Nalanda and Vaishali were significant cities in ancient India, but they were not the capital of Chandragupta Maurya's empire.

The selection of Pataliputra reflected Chandragupta Maurya's vision for a powerful and centralized empire. The city's strategic location and infrastructure provided the necessary foundation for his ambitious administrative and economic policies. It served as a hub for the political, economic, and social life of the empire. The city's growth and importance during his reign cemented Pataliputra's position as a prominent city in ancient Indian history.