Misc: In 1975 Jack Nicholson won the best actor Oscar for his role in this film?

Questions

Which word means the minimum number who must attend a meeting to make it valid?

In computing which letter of the alphabet represents 1,024 bytes?

Who is the only female tennis player to win the grand Slam and an Olympic gold medal in the same year?

The Stone of Scone is a relic sacred to which country?

Which English river has the same name as a Russian one?