What is the most successful album made by Queen?

Queen's most successful album is A Night at the Opera, released in 1975. It was a critical and commercial success, topping the charts in the UK and the US, and selling over six million copies in the US alone. The album features some of Queen's most iconic songs, including "Bohemian Rhapsody," "You're My Best Friend," and "Love of My Life." It is considered one of the greatest albums of all time, and has been certified quadruple-platinum by the RIAA.