Which one is an ore of sodium?

$2\underset{\mathrm{s}}{\mathrm{PbO}} + \underset{\mathrm{s}}{\mathrm{C}} \to 2\underset{\mathrm{s}}{\mathrm{Pb}} + 2\underset{\mathrm{g}}{{\mathrm{CO}}_2}$

Which of the following statements are correct for the above chemical reaction?

(i) Lead is reduced.

(ii) Carbon di oxide is oxidised.

(iii) Carbon is oxidised.

(iv) Lead oxide is reduced

Consider the electrochemical cells(I and II) shown in the following figures and select the correct statement about these cells 

$2\mathrm{Al} + 2{\mathrm{Fe}}_2{\mathrm{O}}_3\to {\mathrm{Al}}_2{\mathrm{O}}_3+2\mathrm{Fe}$

($\mathrm{Al}=27\mathrm{u}, \mathrm{Fe}=56\mathrm{u}, \mathrm{O}=16\mathrm{u}$ are the atomic masses)

How much of Iron, we can get if 54 kg of Aluminium is used?

Give one word or a phrase for the following statement:

• Electrode used as a cathode in electrorefining of impure copper.

During electrolytic production of aluminium, the carbon anodes are replaced from time to time because