Study the flowchart given and give balanced equations to represent the reactions A, B and C

$\text{Mg}$3\text{N}2 \xrightarrow{\text{A}} \text{NH}3 \xtofrom[\text{C}]{\text{B}} \text{NH}4\text{Cl}

Name the gas evolved when : Ammonia reacts with heated copper [II] oxide.

Fill in the blank with the choices given in the bracket: Ammonia reacts with excess chlorine to form ……………. [nitrogen / nitrogen trichloride / ammonium chloride]

State one observation for the following : Ammonia gas is passed over heated copper [II] oxide.