Under which of the following rulers did Delhi first became a capital?

The correct answer is Option 4- Tomara Rajputs

Delhi first became the capital of a kingdom under the Tomara Rajputs. The Tomara Rajputs ruled over the Delhi region from the 8th to the 12th centuries. They were a powerful and prosperous dynasty, and they built many temples and other monuments in Delhi.

The other options are incorrect:

• The Chauhans of Ajmer ruled over the Delhi region from the 12th to the 13th centuries, after the fall of the Tomara Rajputs.
• Iltutmish was the third sultan of the Delhi Sultanate, which was founded in 1206.
• The Khilji dynasty was the second dynasty to rule the Delhi Sultanate, from 1290 to 1320.