Which of the following is correct about Nagara or North Indian Temple…

The correct answer is Option (4) → The garbhagriha is always located directly under the tallest tower.

Out of the options you listed, only one is characteristic of Nagara or North Indian Temple Style Architecture:

• The garbhagriha is always located directly under the tallest tower.

Here's why the other options are incorrect:

• There were no tower or shikhara: Incorrect. Nagara temples are known for their tall, pyramidal towers called shikharas.
• It has elaborate boundary walls: Incorrect. Unlike South Indian temples, Nagara temples typically don't have elaborate boundary walls.
• There was no Kalasha, the topmost part of the temple: Incorrect. The kalasha is a bulbous finial that sits on top of the shikhara, a characteristic feature of Nagara temples.