music: 70's Chart Toppers: Name The Artist: Don't Play That Song?

Questions

Amedeo Avogadro, made famous by picking 6.022 x 10 ^ 23?

Capt. Cook passes through Bering Strait.?

The US-Canada border defined by the Webster-Ashburton Treaty.?

Hungarian Republic crushed by Austria and Russia.?

Henry David Thoreau published `Walden'.?