United Nations Day, marking the entry into force of the UN Charter, is celebrated every year on which date?

Introduction / Context:
United Nations Day is an important international observance that marks the formal entry into force of the UN Charter and the birth of the United Nations as a global organisation. Knowledge of this date is frequently tested in general studies and international organisations sections of competitive exams. It helps candidates connect historical events such as the end of the Second World War with the formation of global governance institutions.

Given Data / Assumptions:

• The question asks for the date on which United Nations Day is celebrated every year.
• It is directly related to the entry into force of the UN Charter.
• Four different dates spread across the year are provided as options.
• We assume the candidate is familiar with basic facts about the United Nations and its history.

Concept / Approach:
The UN Charter came into force on 24 October 1945, after being ratified by the required number of signatory states. As a result, 24 October is celebrated each year as United Nations Day to highlight the roles and achievements of the organisation. The approach to solving this question is straightforward factual recall: link the date of the Charter becoming effective with the observance day. Remembering year 1945 and date 24 October together helps reinforce the fact.

Step-by-Step Solution:
Step 1: Identify that the question is about United Nations Day and not about any other UN related week or decade. Step 2: Recall that the United Nations as an organisation formally came into existence when its Charter entered into force. Step 3: Remember the key fact that this happened on 24 October 1945. Step 4: Link this historical date with the annual observance known as United Nations Day. Step 5: Choose option C, 24 October, as it matches both the historical event date and the annual observance date.

Verification / Alternative check:
This fact can be cross checked using standard international organisations chapters in Polity or GK books, where the founding of the United Nations is usually described in detail. The date 24 October appears as United Nations Day in most exam oriented lists of important days. Official UN websites and UN Day messages by world leaders also highlight 24 October, confirming that this is a stable and well established observance date. Repeated exposure to this information through multiple reputable sources provides strong verification.

Why Other Options Are Wrong:
Option A, 7 April, is associated with World Health Day, which is linked to the World Health Organization, not the United Nations as a whole.
Option B, 25 August, does not correspond to the founding date of the United Nations or any major UN wide observance, so it is incorrect here.
Option D, 27 December, is unrelated to the entry into force of the UN Charter and should therefore be rejected for this question.

Common Pitfalls:
A common mistake is to confuse United Nations Day with Human Rights Day or other UN related observances that fall in December. Another pitfall is to remember the year 1945 correctly but forget the exact date, leading to guesswork among options that are spread across the year. To avoid this, many students link the date 24 October with the idea of post war rebuilding and the start of formal international cooperation under the UN umbrella. Writing small flash cards for major organisations and their founding dates can also help in long term retention.

Final Answer:
United Nations Day is celebrated every year on 24 October.