Question

Ammonia is a base but does not contain a hydroxide group

Answer 1

well the molecular formula of Ammonia is (NH3) and this is important thing
and it has a lone pair of electrons on Nitrogen atom 
And by lewis theory we know that , the acid is an acceptor of electrons while the base donates the electron pair
Here in ammonia due to presence of lone pair of electron when it is added to water , it releases its lone pair to water (hydroxide ion) and in return it gets a proton from water to form a positive ion NH4+ ion. hence it is basic in nature
Hope this helped you
:-)

Answer 2

Answer:

refer to the above attachment