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

H2O, NH3, OH, NH2



• Ammonia is more basic than water because NH3 has less electronegative central atom N (rather than O), therefore it’s tendency of holding onto electrons is much less than oxygen and it is better electron donor i.e. better base than H2O.


• When it comes to the basic strength order NH2 > OH , conjugate acid-base pair concept must be taken into account i.e. the stronger the acid, the weaker will be the conjugate base.


• NH2 and OH both of the species are the conjugate bases of NH3 and H2O respectively.


• As H2O is a stronger acid than NH3 (due to stronger proton donating ability of the former), H2O autoionizes itself but NH3 shows reluctance in donating protons.



• Therefore, conjugate base of water i.e. OH must be a weaker base ( water is stronger acid)thanNH2 (as ammonia is weaker acid).


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