Short answers, pulled from the story.
John Lennon wrote the song on the 20th of January 1970 after returning to the UK from Denmark. He developed the melody for the composition within an hour while working at home on a piano.
The recording session took place at EMI Studios in north-west London on the evening of the 27th of January 1970. Phil Spector produced the track using his signature Wall of Sound technique with George Harrison, Klaus Voormann, Alan White, and Billy Preston.
Lennon and Ono staged a publicity stunt at the Black Centre in north London where they donated a large plastic bag full of their hair to black power activist Michael X. In return they received Muhammad Ali's bloodstained boxing shorts and promised to auction the shorn hair for charity.
Instant Karma peaked at number 3 on America's Billboard Hot 100 chart and reached number 5 on the UK Singles Chart. The Recording Industry Association of America certified it gold on the 14th of December 1970 making it Lennon's sole RIAA-certified gold single until his death.
Artists who have covered Instant Karma include Toad the Wet Sprocket, Paul Weller, Duran Duran, U2, and Bleachers. Stephen King took the title from Lennon's line We all shine on for his 1977 horror novel The Shining while Flaming Lips recorded I Don't Understand Karma as a reply in 2009.