Efimova brings Russia second medal of the day
Tuesday's 100-meter breaststroke winner Soni led from start to finish and stopped the clock at 2 minutes and 21.47 seconds.
Nineteen- year-old Yulya Efimova of Russia won the silver with the magic time of 2 minutes and 22.22 seconds.
Canada's Martha McCabe finished third in 2:24.81 to take bronze. Her compatriot, defending champion and world record holder Annamay Pierse, finished eighth.
Also on Friday, Olympic Champs the United States’ men’s 4x200-meter freestyle relay team, anchored by Ryan Lochte, won gold, leaving France and China in their wake.
Jeanette Ottesen of Denmark and Aleksandra Herasimenia shared gold in the women's 100-meter freestyle.
While Daniel Gyurta of Hungary overtook Olympic Champion Kosuke Kitajima on the final lap to win gold in the men’s 200-meter breaststroke.