HCl (aq) + NH3 (aq) ----- > NH4Cl (s) as the reaction is an acid-base reaction. You can use the equation H+ + OH- -----------> H20 as its ionic equation.
Brass is an alloy which contains copper. When brass is reacted with concentrated
nitric acid a solution containing Cu2+ ions is produced. As an acid contains Hydroxide ions it reacts with them to produce copper hydroxide.
P.S. If the ionic equation confuses you then here's what actually happens in the reaction.
NH3 + H2O = NH4+ + OH- (As it is ammonia "solution"
NH4+ + OH- +H+ +Cl- =NH4+ + Cl- + H2O (A result of reaction with HCl)
As NH4+ and Cl- are in both parts of the equation we can disregard them.
But in your O levels only writing the main equation will suffice.