The capital of Qutbuddin Aibak was:

Explanation

After the death of Muhammad Ghori (1206 AD), the notable people and amirs of Lahore invited Qutb-ud-din Aibak to assume sovereign powers. Therefore, he went to Lahore, assumed power, and was formally enthroned in 1206 AD. Aibak’s capital was Lahore. After ascending the throne, Aibak’s biggest challenge came from Taj-ud-din Yalduz and Nasir-ud-din Qubacha—Ghori’s slaves and successors/claimants to his territories. Aibak married his daughter to Qubacha and thus brought him to his side; however, the threat from Yalduz continued. This is why Aibak always stayed in Lahore. He never got an opportunity to go to Delhi.