Explanation:
The United Nations is an intergovernmental organization that aims to maintain international peace and security, promote human rights, and foster international cooperation. It has several organs that work together to achieve these objectives. The chief organs of the United Nations Organisation are:

a) General Assembly: It is the main deliberative body of the United Nations, consisting of representatives of all member states. It meets annually to discuss and coordinate international issues, adopt resolutions, and approve the budget of the United Nations.

b) Security Council: It is responsible for maintaining international peace and security. It has 15 members, including five permanent members (China, France, Russia, the United Kingdom, and the United States) and ten non-permanent members elected for two-year terms.

c) International Court of Justice: It is the principal judicial organ of the United Nations, with the mandate to settle legal disputes between states and to give advisory opinions on legal questions referred to it by the United Nations organs.

d) Economic and Social Council: It is responsible for promoting international economic and social cooperation, and for formulating and coordinating policies and programs in these areas.

e) Secretariat: It is responsible for carrying out the day-to-day work of the United Nations, under the guidance of the Secretary-General.

The International Labour Organisation (ILO) is a specialized agency of the United Nations that deals with labor issues. While it works closely with the United Nations, it is not a chief organ of the United Nations Organisation. Therefore, option A is the correct answer.