A little to young to tell by the first picture roo, But the comb could be a hen. How old is She/ He is he/she starting to make a slight crowing in its throat? It will sometimes sound like it is choking
I just went through the same thing with 3 RIRs. Couldn't tell, read all the blogs, tips and websites. Then stumbled upon this tip: when they are chicks, if there is a dark spot OR better yet, a dark thin stripe down center if baby's head, it's a girl.
At 12 weeks, we suspected we had two Roos and one pullet. Went back to pics from 2/3 weeks old. Sure enough, one had a stripe and the other 2 did not. Days later the two suspects started making awkward crowing sounds. Bummer!