On This Day: 18 May 1974 India becomes 6th nation to explode an ---------- ?

Questions

who had a major hit with joni mitchell's 'both sides now'?

who is the chief of lamaism in tibet and mongolia?

who was lord mayor of london in 1398, 1406 and 1419, and is most famous for his legendary cat?

air is 21% oxygen 78% ______ and 1% other gases?

until when was california a part of mexico?