Ag+(aq)+2NH3(aq)⇌Ag(NH3)2+(aq) : A g + ( a q ) + 2 N H 3 ( a q ) ⇌ A g ( N H 3 ) 2 + ( a q ) : blank is the Lewis acid and blank is the Lewis base. is the Lewis acid and A g + ( a q ) + 2 N H 3 ( a q ) ⇌ A g ( N H 3 ) 2 + ( a q ) : blank is the Lewis acid and blank is the Lewis base. is the Lewis base.

Silver ion - Lewis acid, Ammonia -  Lewis base

Explanation:

The reaction is given as;

Ag+(aq) + 2NH3(aq) ⇌ [Ag(NH3)]2+(aq)

A lewis acid is an electron pair acceptor. While a lewis base is any substance that that can donate a pair of nonbonding electrons.

This reaction however is a complexation reaction, where ammonia is reacting with the silver ion.

Silver ion accepts electrons in this reaction, hence it is the lewis acid. The ammonia on the other hand donates the electrons used in bonding so it is the lewis base.