Short answers, pulled from the story.
The Russian Empire was established in November 1721, when Peter I was granted the title of Imperator following the Treaty of Nystad. It ended in September 1917 with the proclamation of the Russian Republic after Nicholas II abdicated during the February Revolution.
At its height in the late 19th century, the Russian Empire covered about 22,800,000 square kilometres, roughly one-sixth of the world's landmass. It was the third-largest empire in history, behind only the British and Mongol empires.
The Russian Empire conducted only one census, in 1897, which recorded a population of 125.6 million people. By 1914, that population had grown to approximately 164 million.
A combination of catastrophic military defeats in World War I, food and fuel shortages, mounting inflation, and mass strikes culminated in the February Revolution. On the 8th of March 1917, protests in Petrograd drew hundreds of thousands of people; 80,000 troops sent to suppress them refused orders. Nicholas II abdicated, and the Russian Republic was proclaimed on the 1st of September 1917.
Alexander II issued the Emancipation Reform of 1861, freeing all serfs. At the time, there were more than 23 million serfs. The freed peasants were required to pay a special lifetime tax in exchange for land, which was owned collectively by the village community known as the mir.
Russia sold Alaska in 1867 because it viewed the territory as indefensible. The sale price was 11 million rubles, equivalent to 7.2 million dollars, paid by Andrew Johnson's government. The deal was brokered by Secretary of State William H. Seward, and many Americans initially called it "Seward's Folly" before gold and petroleum were later discovered there.