Officially, what is the full conventional long name of the country Sri Lanka according to its constitution and international usage?

Introduction / Context:
This question checks knowledge of the formal constitutional names of countries, not just their short or commonly used forms. Many states have an official long name that conveys their political system, such as democratic republic, socialist republic, or kingdom, while the short name omits these descriptive words. For Sri Lanka, examinations often test whether candidates know the precise official title as used in legal and diplomatic contexts.

Given Data / Assumptions:

• The question asks for the official conventional long name of Sri Lanka.
• Options include several similar forms: Democratic Socialist Republic of Sri Lanka, Socialist Republic of Sri Lanka, Republic of Sri Lanka, and some additional distractor formulations.
• We assume standard general knowledge of world countries and their constitutional structures.

Concept / Approach:
The approach is to recall that Sri Lanka adopted a republican constitution and later described itself officially as a democratic socialist republic. This reflects both its democratic framework and its commitment at the time to a form of socialism. The exact phrase Democratic Socialist Republic of Sri Lanka appears in official documents and in the constitution. The task is to distinguish this precise phrase from similar looking but incomplete names in the options.

Step-by-Step Solution:
Step 1: Recall that many countries have long official names which combine political and economic descriptions. Step 2: For Sri Lanka, remember that it is not simply a republic but is officially described as a democratic socialist republic. Step 3: Look at the options and locate the one that matches the full phrase Democratic Socialist Republic of Sri Lanka. Step 4: Compare it with other options like Socialist Republic of Sri Lanka or Republic of Sri Lanka, which are shorter and do not include the full constitutional term. Step 5: Select Democratic Socialist Republic of Sri Lanka as the correct answer.

Verification / Alternative check:
To verify, you can refer to the preamble of the constitution of Sri Lanka or to standard world fact books issued by reputable organisations. These sources clearly list the country under its long form as Democratic Socialist Republic of Sri Lanka and its short form as Sri Lanka. Diplomatic documents, official websites, and international reference works consistently use this full title in formal contexts. Since none of the other options match this exact phrasing, this cross check confirms the correctness of option A.

Why Other Options Are Wrong:
Socialist Republic of Sri Lanka: This omits the word Democratic, which is a key part of the official title, therefore it is incomplete and incorrect.
Republic of Sri Lanka: This is a shortened form that ignores both democratic and socialist descriptors, so it is not the full long name asked in the question.
Kingdom of Sri Lanka: Sri Lanka is not a monarchy in the modern period and is not officially described as a kingdom, so this option is wrong.
Union of Sri Lanka: This is not an official or commonly recognised formal name, hence it is incorrect.

Common Pitfalls:
Candidates sometimes skim the options and choose Republic of Sri Lanka because it looks familiar and simple, without noticing that the question demands the conventional long name. Another pitfall is confusion with other countries that use the phrase Socialist Republic or Democratic Republic. Some learners may also think that including fewer words makes the name more modern, but in reality constitutions often retain detailed historical formulations. Careful reading of both question and options helps avoid these mistakes.

Final Answer:
The official conventional long name of Sri Lanka is Democratic Socialist Republic of Sri Lanka.