The state is more than its current government.
A federal government pursues political projects and is accountable to the Bundestag. The head of state represents the Federal Republic and performs separate functions set out in the Basic Law.
This distinction helps when reading international news: a visit by Germany's head of state and a meeting with its head of government may concern two different people.

The other three answers
The other officeholders head different constitutional institutions.
the Federal Chancellor
The Federal Chancellor is head of government. In Germany, that office is separate from the head of state.
the President of the Bundesrat
The President of the Bundesrat chairs that institution. Under Article 57, this person can perform presidential functions in specified circumstances, but does not thereby become the regular holder of the Federal Presidency.
the President of the Bundestag
The President of the Bundestag presides over parliament. That parliamentary presidency is not the office of head of state.
Acting for someone is not the same as holding a new office.
Article 57 provides that the Bundesrat President exercises presidential powers when the Federal President is unable to act or the office ends prematurely. This is a substitution rule, not a reason to replace the ordinary test answer.
This question asks for the office title, not a current personal name. A change of officeholder therefore does not automatically alter the correct answer.
Role in the state · Office of the Federal President ↗Head of state = Federal President. Head of government = Federal Chancellor.
Learn the pair of roles together to avoid swapping the titles.
Three words for this question
- das Staatsoberhaupthead of state
- The highest representative state office; in Germany, the Federal Presidency.
- der Regierungschefhead of government
- The person leading the government.
- die Vertretungacting on behalf of another officeholder
- Temporarily performing functions under an established rule.
