Which of the following Sultan is believed to have completed the construction of Qutub Minar?

Iltutmish

The correct answer is Option 4- Iltutmish

The Qutub Minar was constructed in 1192 by Qutb-ud-din Aibak,and later completed by his successor Iltutmish.

The Qutub Minar is a towering monument and a UNESCO World Heritage Site located in the Mehrauli area of South Delhi, India.  
It was built between 1199 and 1220, primarily by Qutub-ud-din Aibak, the first Sultan of Delhi. Construction was later continued by his successor, Iltutmish.
Initially it was conceived as a "victory tower" to commemorate the Qutub dynasty's triumph over Hindu kingdoms.
It is constructed primarily of red sandstone with some elements in buff sandstone and marble.
Standing tall at 72.5 meters (237.8 feet), it's the tallest brick minaret in the world.
379 steps lead up to the balconies and the top, offering a panoramic view of Delhi.