In aniline, basicity is due to resonance effects that release electrons. In orthochloro aniline and metachloro aniline, there are both resonance and inductive effects at play. Resonance effects increase basicity more at the ortho position than the meta position, while inductive effects decrease basicity. Therefore, aniline is most basic, followed by orthochloroniline, with metachloroaniline being the least basic.