Which of the following pairs is correctly matched?

Steel becomes soft and pliable by:

Blister copper is refined by stirring molten impure metal with green logs of wood because such wood liberates hydrocarbon gases (like $CH_4$). This process $X$ is called . . . . . . . . . and the metal contains impurities of $Y$ is . . . . . . . . .

Zone refining is based on the principle of

Refining of tin cannot be done by

Name the common elements present in the anode mud in electrolytic refining of copper. Why are they so present?