In the Constitution of the United States of America, citizenship is explicitly defined and protected in which one of the following amendments?

Introduction / Context:
Knowledge of key constitutional provisions is a common theme in general knowledge and civics examinations. In the case of the United States, several amendments form the foundation of civil rights and citizenship law. The amendment that clearly defines who is a citizen of the United States and provides equal protection under the law is especially important.

Given Data / Assumptions:

• The question asks which amendment to the United States Constitution defines citizenship.
• Options include the 10th, 11th, 12th, and 14th Amendments.
• We assume familiarity with broad themes of these amendments, not every detail.

Concept / Approach:
The 14th Amendment, adopted after the American Civil War, contains the Citizenship Clause. This clause states that all persons born or naturalised in the United States and subject to its jurisdiction are citizens of the United States and of the state where they reside. It also includes the Due Process and Equal Protection Clauses, which are central to civil rights jurisprudence. The 10th Amendment deals with powers reserved to the states, the 11th Amendment addresses suits against states, and the 12th Amendment modifies procedures for electing the president and vice president. None of these define citizenship.

Step-by-Step Solution:
Step 1: Recall that post Civil War amendments, especially the 13th, 14th, and 15th, focused on ending slavery and protecting the rights of formerly enslaved people.Step 2: Identify that the specific constitutional definition of national and state citizenship is found in the 14th Amendment.Step 3: Note that the 10th Amendment in the Bill of Rights is about reserved powers, not citizenship.Step 4: Recognise that the 11th Amendment concerns judicial limits and state sovereign immunity, and the 12th Amendment reforms the Electoral College system.Step 5: Conclude that the only correct option for defining citizenship is the 14th Amendment.

Verification / Alternative check:
Standard civics and constitutional law summaries always mention the 14th Amendment when discussing the legal meaning of United States citizenship and the Equal Protection Clause. If you recall that landmark civil rights decisions rely heavily on the 14th Amendment, it further confirms that this is the correct answer for a question about where citizenship is defined in the Constitution.

Why Other Options Are Wrong:
The 10th Amendment confirms that powers not delegated to the federal government are reserved to the states or the people. The 11th Amendment deals with the jurisdiction of federal courts in suits against states. The 12th Amendment refinements concern presidential elections and vice presidential selection. None of these contain the fundamental definition of citizenship, so they are not correct for this question.

Common Pitfalls:
Some candidates may confuse the numerical order of amendments or may think the Bill of Rights (first ten amendments) directly defines citizenship. Others may not distinguish between rights protections and citizenship definitions. Remembering that the famous equal protection and citizenship clauses are anchored in the 14th Amendment prevents such confusion in exam settings.

Final Answer:
Citizenship in the United States Constitution is explicitly defined in the 14th Amendment.