The #1 on Music Bank on 2012-09-07 was “Pandora” by Kara — win No. 1 for the song and career win No. 1 for Kara (No. 1 on this show).
“Pandora” has 2 music show wins in total: 2012-09-07 Music Bank, 2012-09-13 M Countdown. Kara had 1 wins in 2012 up to this date, and this was the artist's first win on Music Bank. The previous week's Music Bank #1 was “Gangnam Style” by Psy. Episode data comes from broadcasters' published results (Wikipedia lists, CC BY-SA) and is recounted daily.