Final answer:
The United Nations Service Medal was authorized in 1950 to reward participation in UN peacekeeping operations, following the establishment of the UN to promote peace after World War II.
Step-by-step explanation:
The United Nations Service Medal was authorized in 1950. This medal is awarded to military personnel and civilian police who have participated in United Nations peacekeeping operations. The creation of the United Nations itself was in response to promote international peace following the devastation of World War II. The goal was to prevent future conflicts of such a scale. Therefore, the correct answer to the question 'Which year was the United Nations Service Medal authorized?' is 1950 (option b).