The capital of the Avanti Mahajanapada (northern Avanti) was:

The capital of the Avanti Mahajanapada was Ujjayini (Ujjain), in present-day Madhya Pradesh.

About Avanti:

• It was one of the four most powerful Mahajanapadas, along with Magadha, Kosala and Vatsa.
• It was located in the Malwa region of western Madhya Pradesh.

It was divided into two parts by the Vindhya range:

• Northern Avanti, with its capital at Ujjayini.
• Southern Avanti, with its capital at Mahishmati (on the Narmada).
• Its most famous king was Chanda Pradyota (Pradyota Mahasena), a contemporary of the Buddha and of Bimbisara.
• He was a powerful and aggressive ruler, who had conflicts with the kings of Vatsa and Magadha.
• Avanti was eventually conquered by Magadha under the Shishunaga dynasty.

About Ujjayini:

• It is located on the banks of the Kshipra river.
• It was an important centre of trade, on the route from the north to the western ports.
• In the Mauryan period, it was the headquarters of a province; according to tradition, Ashoka served as governor of Ujjain before becoming emperor.
• It was later an important city of the Shakas (Western Kshatrapas) and the Guptas.
• It was a great centre of learning, astronomy and culture; the prime meridian of ancient Indian astronomy passed through Ujjain.
• The poet Kalidasa is associated with Ujjain.

Ujjain today:

• It is one of the seven sacred cities (Saptapuri) of Hinduism.
• It has the Mahakaleshwar temple, one of the 12 Jyotirlingas.
• The Simhastha Kumbh Mela is held here every 12 years.
• The Vedh Shala (observatory) built by Sawai Jai Singh II is located here.

Why not the other options?

• ✗Mahishmati was the capital of southern Avanti.
• ✗Kaushambi was the capital of Vatsa.
• ✗Vidisha was an important city of the Malwa region, but not the capital of Avanti.