The correct decreasing order of basic strength of the following species is.


1. NH2>OH>NH3>H2O
2. OH>NH2>H2O>NH3
3. NH3>H2O>NH2>OH
4. H2O>NH3>OH>NH2

HINT: Conjugate acid-pair strength
The basic strength of the above species can be explained on the basis of the electronegativity of the central atom and its proton-accepting tendency. Here, amide ion is most basic among given compounds due to the presence of negative charge and two pairs of electrons on the nitrogen atom.