Which kind of impurities are present in the ores? What are these impurities collectively known as?

An electrolytic cell consists of
$(i)$ positively charged cathode
$(ii)$ negatively charged anode
$(iii)$ positively charged anode
$(iv)$ negatively charged cathode

Define alloys. List the properties of alloys that make them useful over pure metals. Explain this fact with suitable examples.

Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
$(i)$ $Au$
$(ii)$ $Cu$
$(iii)$ $Na$
$(iv)$ $K$

Compound $X$ and aluminium are used to join railway tracks.
$(a)$ Identify the compound $X$.
$(b)$ Name the reaction.
$(c)$ Write down its chemical reaction.

Write chemical equations for the reactions taking place when:
$(i)$ iron is strongly heated in air.
$(ii)$ lead carbonate is calcined.
$(iii)$ chromium oxide $(Cr_{2}O_{3})$ is heated with aluminium powder.