What chapter in Hana Kimi is she revealed as a girl?

Im on Vol.4 chp 17 of Hana Kimi and its driving nuts that shes not aware the guys know shes a girl or that the guys that like her know shes a girl. I want to know when she either finds out Sano Izumi knows shes a female or tells him. And when does other characters. Im just tired of reading chp after chp with no progress :/