The capital of Idar princely state was located at:

Himmatnagar
Idar
Vadnagar
Palanpur

The correct answer is: Idar.

Idar was a princely state in the Kathiawar Agency of British India. It was founded in 1401 by Rao Jodha, the son of Rao Jodha of Marwar. The capital of Idar was located at Idar, which is now a city in Gujarat, India.

Himmatnagar is a city in Gujarat, India. It is the headquarters of Himmatnagar district.

Vadnagar is a city in Gujarat, India. It is the birthplace of Mahatma Gandhi.

Palanpur is a city in Gujarat, India. It is the headquarters of Palanpur district.