In the list of important international observances, October 24 is celebrated worldwide as which of the following days?

Introduction / Context:
This question asks about a key date linked with the United Nations. October 24 is an important date in international relations because on this day the United Nations Charter came into force. As a result, October 24 is observed worldwide as United Nations Day. Examinations often test knowledge of this date in the important-days and organisations section.

Given Data / Assumptions:

• The date mentioned is October 24.
• The options include World Vegetarian Day, United Nations Day, World Immunization Day, and World Environment Day.
• We must recall which observance correctly matches 24 October.

Concept / Approach:
To answer, recall that the UN Charter came into force on 24 October 1945. Since then, this day has been celebrated as United Nations Day to highlight the role of the UN in maintaining peace and cooperation among nations. World Environment Day is held on 5 June, World Vegetarian Day is observed on 1 October, and World Immunization Day is generally marked on 10 November in many GK references. Therefore, only one of the listed options fits October 24.

Step-by-Step Solution:
Step 1: Identify that the question focuses on the specific date 24 October. Step 2: Recall that 24 October marks the coming into force of the United Nations Charter in 1945. Step 3: Because of this historical event, the date is observed as United Nations Day. Step 4: Compare this with the options: World Vegetarian Day (1 October), United Nations Day (24 October), World Immunization Day (10 November), and World Environment Day (5 June). Step 5: Confirm that among these, only United Nations Day matches 24 October. Step 6: Conclude that the correct answer is United Nations Day.

Verification / Alternative check:
You can cross-check this with any reliable international calendar, UN website, or standard GK book. They clearly mention that United Nations Day is celebrated annually on 24 October to commemorate the establishment of the UN. This confirms the accuracy of our choice beyond simple memory.

Why Other Options Are Wrong:
World Vegetarian Day: Observed on 1 October to promote vegetarianism, not on 24 October.
World Immunization Day: Commonly referenced as 10 November in GK lists, unrelated to 24 October.
World Environment Day: Held on 5 June each year and dedicated to environmental protection, not connected to the founding of the UN.

Common Pitfalls:
Many students confuse United Nations Day with other UN-related observances or mix the date with World Environment Day or other global days. A simple way to remember is that 24 October marks the birth of the UN system in 1945, so it logically becomes United Nations Day. Grouping dates by theme (environment, health, organisations) also helps reduce confusion in exam situations.

Final Answer:
Thus, October 24 is observed worldwide as United Nations Day.