The number of principal organs of UNO is -

The main organs of the UN are the General Assembly, the Security Council, the Economic and Social Council, the Trusteeship Council, the International Court of Justice, and the UN Secretariat.
answer : 6

http://www.un.org/en/sections/about-un/main-organs/

Trusteeship council has ceased to be operational therefore now it has five principle organ
1 Secretariat
2 General Assembly
3 International court of Justice
4 Economic & Social Council
5 Security Council

it has 6 principal organs

There are 6 principal organs of uno
1 Secretariat
2 General assembly
3 International court of justice
4 Economic and social council
5 Security council
6 Trusteeship council

Therefore there are 6 organs (C)

There are 6 principal organs of uno
1 General assembly
2 Secretariat
3 International court of justice
4 Economic and social council
5 Security council
6 Trusteeship council