Which of the following is an obligation of a citizen?

An obligation of a citizen is something that they are required to do as part of their duty to their country. Voting at elections is an obligation of a citizen. It is a civic duty and responsibility to vote, as it allows citizens to have a say in who their leaders are and what policies are put in place. By voting, citizens also help to ensure that the democratic process is upheld and that the government remains accountable to the people. Therefore, the correct option is "Voting at elections".