The correct order of relative basic strength will be
••
N
H3>
••
N
H2−
••
N
H2>
••
N
H2−OH In NH3, the lone pair is completely available for donation, hence is most basic whereas NH2−NH2 and NH2−OH can be considered as derivatives of NH3. Here, H is replaced by −NH2 forming NH2−NH2 and −OH forming NH2−OH being highly electron withdrawing due to −O will "decrease the electron density most on −N. ∴ Least basic electron withdrawing −I-effect of −NH2 is less as compared to −OH. Hence correct order of basic strength is NH3>NH2−NH2>NH2−OH