Explanation:

- The popular style of temple architecture in northern India is called the Nagara style.

- Option 1: Panchayatana – This refers to a temple layout with a main shrine surrounded by four subsidiary shrines. It's not a style but a structural arrangement.

- Option 2: Nagara – This is the correct answer. Nagara is the distinctive style of temple architecture in northern India, recognized by its curvilinear towers (shikharas).

- Option 3: Shikara – This term refers to the rising tower in the temple's architecture, especially in Nagara style, not the architectural style itself.

- Option 4: Dravida – This is the style of temple architecture found predominantly in southern India, characterized by pyramid-shaped towers (vimanas).