Which of the following is not a principal organ of the United Nations?

Correct option is D

The International Human Rights Commission (IHRC) is not one of the six principal organs of the United Nations. The principal organs of the UN, as per the UN Charter, are:
1. General Assembly
2. Security Council
3. Economic and Social Council (ECOSOC)
4. International Court of Justice (ICJ)
5. Trusteeship Council (inactive since 1994)
6. Secretariat