In which of the following countries will the no-confidence motion to bring down the government passed by the legislature be valid only when the legislature is able to find simultaneously a majority to elect a successor government ?

The requirement described is the “constructive vote of no confidence,” under which a legislature may remove the head of government only if it simultaneously elects a successor with an absolute majority. Germany’s Basic Law implements this mechanism: the Bundestag can vote the Chancellor out only by electing a successor (as demonstrated in Helmut Kohl’s 1982 election) and the Chancellor can be removed only through that constructive process. Comparative descriptions of the constructive no-confidence rule explicitly define it as withdrawal of confidence only where a positive majority exists for a prospective successor, ensuring governmental stability by preventing removal without an alternative majority-backed government [1].

Sources

1. [1] https://en.wikipedia.org/wiki/Constructive_vote_of_no_confidence