In comparing hydroxylamine, hydrazine, and methylamine for basicity, the order of increasing basicity is hydroxylamine < hydrazine < methylamine.
I tried to reason this trend based on electron donating power of the -$\ce{OH}$, -$\ce{NH2}$, and -$\ce{CH3}$ groups, however that yields the order of basicity: methylamine < hydroxylamine < hydrazine, because more electron-donating power concentrates electron density on the nitrogen atom, making it more basic.
Other factors, such as steric hindrance, do not seem to be impacting anything here, because $\ce{-OH}$, $\ce{-NH2}$, and $\ce{-CH3}$ groups are all around the same size.
What is the key factor that influences the basicity here? I realize that hydrazine has two nitrogen atoms, whereas hydroxylamine and methylamine have one nitrogen atom, so that may be affecting the basicity.
