Concept:
The United Nations (UN) is an international organization established to maintain international peace, security, cooperation, and friendly relations among nations after World War II.
Step 1: Understand the establishment of the United Nations.
The United Nations was officially established on:
\[
24 \text{ October 1945}
\]
after the signing and ratification of the UN Charter.
Step 2: Identify India's role in the United Nations.
India was among the original founding members of the United Nations.
Even before independence, British India participated in the signing of the UN Charter.
Step 3: Determine the year India joined the UN.
India joined the United Nations in:
\[
1945
\]
thus becoming one of the founding members of the organization.
Step 4: Understand India's contribution to the UN.
India has actively participated in:
• UN peacekeeping missions
• Human rights initiatives
• Sustainable development programmes
• International diplomacy
Step 5: Eliminate incorrect options.
• 1945 -- Correct
• 1946 -- Incorrect
• 1947 -- India became independent in this year
• 1952 -- Incorrect
Step 6: Conclusion.
Therefore, the correct answer is:
\[
\boxed{1945}
\]