In the preparation of aryl halides by Sandmeyer's reaction, name the i) catalyst used ii) gas liberated. 

Explanation

Aromatic primary amines react with nitrous acid at low temperature [273-278K] to form diazonium salt. This reaction is called diazotisation. Freshly prepared diazoniun salt is treated with cuprous chloride to give aryl chloride. This reaction is called Sandmeyer.s reaction.

i) `Cu_(2)Cl_(2)" (Catalyst)"`
ii) Nitrogen (gas is liberated).