Which early plastic did Alexander Parkes develop in the 1850s?

In 1237, the Treaty of York, signed by Alexander II and Henry III, fixed a lasting border between which two kingdoms? Alexander II was called the "Czar Liberator" for freeing which Russian laborers in 1861? Alexander Khalifman, Anatoly Karpov and Garry Kasparov have all been world champions at what? Complete the title of Alexander McCall Smith's 1998 novel: "The No. 1 ___' Detective Agency". Complete Alexander Pope's line: "For fools rush in where angels ___." Alexander Pope wrote that "hope springs eternal in" what? Alexander Pope's 1711 essay in verse was "An Essay on" what? Alexander Popov became the first man to win the Olympic 100-meter freestyle twice since which 1920s swimmer?