Two votes serve different purposes.
The first vote is for a constituency candidate; the second is for a party's state list. The second vote is generally decisive for the balance between parties in the Bundestag.
Seats are allocated using a statutory calculation method. The result must be whole mandates, not fractions of a seat. A small increase in votes therefore need not immediately produce an additional seat.

The other three answers
The question concerns seat shares, not a personal or political obligation.
fewer first votes it can have.
First and second votes are cast separately. More second votes do not automatically reduce first votes.
more direct candidates of the party enter parliament.
A higher second-vote share does not automatically mean more successful constituency candidates. Constituency results and statutory second-vote coverage require separate consideration.
greater the risk of having to form a coalition.
A coalition results from political cooperation after the election. It is not a mathematical risk that must increase with each additional second vote.
Threshold rules are part of the full explanation.
Not every party is included in seat allocation. At the reviewed date, the five-percent threshold applies with the court's transitional rule for parties whose candidates receive the most first votes in at least three constituencies. Parties representing national minorities have a separate exemption.
The test wording summarises the principle. It is not a method for calculating a particular election result; that requires all relevant votes and the applicable allocation rules.
Section 4 · Seat allocation · Federal Elections Act ↗Second vote → party shares → seats.
The first vote selects a constituency candidate; the second shapes the balance in the Bundestag.
Three words for this question
- die Zweitstimmesecond vote
- The vote for a party's state list in a federal election.
- der Stimmenanteilvote share
- A party's proportion of the relevant total votes.
- das Mandatparliamentary seat / mandate
- The position as a member of parliament obtained through an election.
