In civics and world geography, which one of the following responsibilities of United States citizenship is generally considered a legal duty and therefore mandatory when called upon?

Introduction / Context:
Citizenship in any country comes with certain rights and responsibilities. In the United States, some responsibilities are voluntary, while others are legal duties that citizens are required to fulfil when called. This question asks you to identify which responsibility is considered mandatory for United States citizens, an important point in basic civics that often appears in general knowledge exams.

Given Data / Assumptions:

• The context is responsibilities of United States citizenship.
• We must identify the responsibility that is a legal requirement rather than a voluntary activity.
• Options include military service, joining a political party, holding office, and serving on a jury.
• We assume no special emergency laws such as conscription at a given moment.

Concept / Approach:
Core civic duties in the United States include obeying laws, paying taxes, and serving on a jury when lawfully summoned. Jury service is considered a legal obligation, and citizens can face penalties if they ignore a proper call to serve without valid reasons. By contrast, joining a political party or holding office is voluntary, and active duty military service is not compulsory in peacetime. Therefore, the correct answer must be the responsibility that citizens must perform when selected, which is jury service.

Step-by-Step Solution:
Step 1: Examine serving in the army. The United States currently has an all volunteer military, so citizens are not automatically required to serve in the army. Step 2: Look at joining a political party. Political party membership is completely voluntary and is a matter of personal choice. Step 3: Consider holding an elected political office. Many citizens never hold office in their entire life, so this clearly cannot be a mandatory duty. Step 4: Evaluate serving on a jury. When a citizen is selected and summoned for jury duty by a court, that person is legally required to attend or provide a valid excuse. Step 5: Therefore, serving on a jury when lawfully summoned is the mandatory responsibility among the options.

Verification / Alternative check:
Basic civics texts for the United States list paying taxes, obeying laws, and serving on juries as legal duties. They also mention that while citizens are encouraged to vote, stay informed, and participate in public life, those actions are considered important responsibilities but not legal requirements. There is a system of jury selection based on voter registration or driving records, and courts can impose fines or other penalties for unjustified failure to appear. This information confirms that jury duty is the mandatory responsibility highlighted in the question.

Why Other Options Are Wrong:

• Serving in the army on active duty: The draft is not currently active, so military service is voluntary in normal conditions.
• Joining a political party: There is no law requiring citizens to join any party, and many choose to remain independent.
• Holding an elected political office: Only a small number of citizens ever hold office, and it is a voluntary choice.

Common Pitfalls:
Some learners mistakenly assume that serving in the army must be mandatory because of historical drafts in wartime, or they think voting is legally required. Others may confuse encouraged civic participation with legal obligations. To avoid such confusion, always remember that in the United States serving on a jury when called is a clear and specific legal duty of citizenship, while political activities and military service are primarily voluntary in peacetime.

Final Answer:
The responsibility of United States citizenship that is considered mandatory is serving on a jury when lawfully summoned.