¶¶Chahalgani refers to the group of forty important nobles set up by Iltutmish.They were very powerful and were well-known to the Sultan.But after the period of Iltutmish, the power of the Chalgans was put down by Balban.

¶¶ so the option a is correct.

Umara-i Chahalgani was a council that was constituted during the reign of Iltutmish, the third ruler of the Slave Dynasty in India. Let us understand in detail about this council.

Iltutmish and his reign
Iltutmish ascended the throne in 1210 AD after the death of his predecessor Qutubuddin Aibak. He was a capable ruler and expanded his empire by conquering territories in Punjab, Rajasthan, and Bengal. He also introduced several administrative reforms during his reign.

Umara-i Chahalgani
The term Umara-i Chahalgani literally means the group of forty nobles. This council was constituted by Iltutmish and consisted of forty high-ranking officials. The members of this council were appointed by the Sultan and were responsible for advising him on matters of administration and governance.

Functions of the council
The council had several important functions. They were responsible for maintaining law and order in the empire, collecting taxes, and ensuring that the revenue collected was used for the welfare of the people. They also advised the Sultan on matters of foreign policy and diplomacy.

Importance of the council
The council played a crucial role in the administration of the Slave Dynasty. They helped the Sultan in making important decisions and ensured that the policies implemented were in the best interest of the people. The council also helped in maintaining the stability of the empire by preventing any internal or external threats.

Conclusion
Thus, Umara-i Chahalgani was an important council that was constituted during the reign of Iltutmish. The council played a crucial role in the administration of the Slave Dynasty and helped in maintaining law and order in the empire. Its members were responsible for advising the Sultan on matters of governance, foreign policy, and diplomacy.