Final answer:
Queen is the British band that blended Glam Rock and Prog Rock in their 1975 album "A Night at the Opera" featuring the iconic song 'Bohemian Rhapsody'.
Step-by-step explanation:
The British band that successfully blended both Glam Rock and Prog Rock with their breakthrough 1975 album "A Night at the Opera" is Queen. This album includes the hit song 'Bohemian Rhapsody', which is often cited as a milestone for its unique structure, mixing rock balladry, operatic passages, and hard rock elements, showcasing the band's versatility and their ability to cross genre boundaries. Queen's approach to music was innovative, and their elaborate live performances and masterful use of the studio as an instrument set them apart from their peers, solidifying their place in rock history.