What is an alloy called if one of the metals is $Mercury$?

During the electrolytic refining of zinc,it gets :

Which process is used to convert sulphide ores into oxides by heating them in the presence of excess air?

$A$ metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.

State whether the following statement is true or false:
At ordinary temperature,the surfaces of metals such as magnesium,aluminium,zinc,lead,etc.,are covered with a thin layer of oxide which prevents the metal from further oxidation.

Which gas is responsible for acid rain?