You can never be 100% sure, more like 80%. That one, for me is hard to judge, but with the more rounded nose, and circular body, I'm gunna have to go with male. Can someone confirm?
The only SURE WAY of sexing angelfish is watching them spawn. During their spawning, the male will have a much smaller and thinner (almost like a pencil point) tube while the female has a much thicker and larger tube. The tube is located between the ventral and anal fins. There are other ways to sex angelfish for the experienced angelfish breeder but it will never be 100% accurate. Small angelfish are impossible to sex.